diff --git a/data_structures/binary_search_tree_test.ts b/data_structures/binary_search_tree_test.ts
index acfb72e7d33e..4ae14e4f170d 100644
--- a/data_structures/binary_search_tree_test.ts
+++ b/data_structures/binary_search_tree_test.ts
@@ -544,7 +544,7 @@ Deno.test("BinarySearchTree handles README example", () => {
   ]);
 });
 
-Deno.test("BinarySearchTree.max() handles null ", () => {
+Deno.test("BinarySearchTree.max() handles null", () => {
   const tree = BinarySearchTree.from([1]);
   assert(!tree.isEmpty());
   tree.clear();
diff --git a/data_structures/deno.json b/data_structures/deno.json
index 44e17d084998..52b9617b65fd 100644
--- a/data_structures/deno.json
+++ b/data_structures/deno.json
@@ -6,6 +6,7 @@
     "./unstable-bidirectional-map": "./unstable_bidirectional_map.ts",
     "./binary-heap": "./binary_heap.ts",
     "./binary-search-tree": "./binary_search_tree.ts",
+    "./unstable-binary-search-tree": "./unstable_binary_search_tree.ts",
     "./comparators": "./comparators.ts",
     "./red-black-tree": "./red_black_tree.ts"
   }
diff --git a/data_structures/unstable_binary_search_tree.ts b/data_structures/unstable_binary_search_tree.ts
new file mode 100644
index 000000000000..147c11a99dda
--- /dev/null
+++ b/data_structures/unstable_binary_search_tree.ts
@@ -0,0 +1,382 @@
+// Copyright 2018-2025 the Deno authors. MIT license.
+// This module is browser compatible.
+
+import type { BinarySearchNode, Direction } from "./_binary_search_node.ts";
+import { BinarySearchTree as StableBinarySearchTree } from "./binary_search_tree.ts";
+import { internals } from "./_binary_search_tree_internals.ts";
+
+const {
+  getRoot,
+  setRoot,
+  setSize,
+  getCompare,
+} = internals;
+
+/**
+ * An unbalanced binary search tree. The values are in ascending order by default,
+ * using JavaScript's built-in comparison operators to sort the values.
+ *
+ * For performance, it's recommended that you use a self-balancing binary search
+ * tree instead of this one unless you are extending this to create a
+ * self-balancing tree. See {@link RedBlackTree} for an example of how BinarySearchTree
+ * can be extended to create a self-balancing binary search tree.
+ *
+ * | Method        | Average Case | Worst Case |
+ * | ------------- | ------------ | ---------- |
+ * | find(value)   | O(log n)     | O(n)       |
+ * | insert(value) | O(log n)     | O(n)       |
+ * | remove(value) | O(log n)     | O(n)       |
+ * | min()         | O(log n)     | O(n)       |
+ * | max()         | O(log n)     | O(n)       |
+ *
+ * @example Usage
+ * ```ts
+ * import {
+ *   BinarySearchTree,
+ *   ascend,
+ *   descend,
+ * } from "@std/data-structures";
+ * import { assertEquals } from "@std/assert";
+ *
+ * const values = [3, 10, 13, 4, 6, 7, 1, 14];
+ * const tree = new BinarySearchTree<number>();
+ * values.forEach((value) => tree.insert(value));
+ * assertEquals([...tree], [1, 3, 4, 6, 7, 10, 13, 14]);
+ * assertEquals(tree.min(), 1);
+ * assertEquals(tree.max(), 14);
+ * assertEquals(tree.find(42), null);
+ * assertEquals(tree.find(7), 7);
+ * assertEquals(tree.remove(42), false);
+ * assertEquals(tree.remove(7), true);
+ * assertEquals([...tree], [1, 3, 4, 6, 10, 13, 14]);
+ *
+ * const invertedTree = new BinarySearchTree<number>(descend);
+ * values.forEach((value) => invertedTree.insert(value));
+ * assertEquals([...invertedTree], [14, 13, 10, 7, 6, 4, 3, 1]);
+ * assertEquals(invertedTree.min(), 14);
+ * assertEquals(invertedTree.max(), 1);
+ * assertEquals(invertedTree.find(42), null);
+ * assertEquals(invertedTree.find(7), 7);
+ * assertEquals(invertedTree.remove(42), false);
+ * assertEquals(invertedTree.remove(7), true);
+ * assertEquals([...invertedTree], [14, 13, 10, 6, 4, 3, 1]);
+ *
+ * const words = new BinarySearchTree<string>((a, b) =>
+ *   ascend(a.length, b.length) || ascend(a, b)
+ * );
+ * ["truck", "car", "helicopter", "tank", "train", "suv", "semi", "van"]
+ *   .forEach((value) => words.insert(value));
+ * assertEquals([...words], [
+ *   "car",
+ *   "suv",
+ *   "van",
+ *   "semi",
+ *   "tank",
+ *   "train",
+ *   "truck",
+ *   "helicopter",
+ * ]);
+ * assertEquals(words.min(), "car");
+ * assertEquals(words.max(), "helicopter");
+ * assertEquals(words.find("scooter"), null);
+ * assertEquals(words.find("tank"), "tank");
+ * assertEquals(words.remove("scooter"), false);
+ * assertEquals(words.remove("tank"), true);
+ * assertEquals([...words], [
+ *   "car",
+ *   "suv",
+ *   "van",
+ *   "semi",
+ *   "train",
+ *   "truck",
+ *   "helicopter",
+ * ]);
+ * ```
+ *
+ * @typeparam T The type of the values stored in the binary search tree.
+ */
+export class BinarySearchTree<T> extends StableBinarySearchTree<T> {
+  /**
+   * Construct an empty binary search tree.
+   *
+   * To create a binary search tree from an array like, an iterable object, or an
+   * existing binary search tree, use the {@link BinarySearchTree.from} method.
+   *
+   * @param compare A custom comparison function to sort the values in the tree.
+   * By default, the values are sorted in ascending order.
+   */
+  constructor(compare?: (a: T, b: T) => number) {
+    super(compare);
+  }
+
+  /**
+   * Creates a new binary search tree from an array like, an iterable object,
+   * or an existing binary search tree.
+   *
+   * A custom comparison function can be provided to sort the values in a
+   * specific order. By default, the values are sorted in ascending order,
+   * unless a {@link BinarySearchTree} is passed, in which case the comparison
+   * function is copied from the input tree.
+   *
+   * @example Creating a binary search tree from an array like
+   * ```ts no-assert
+   * import { BinarySearchTree } from "@std/data-structures";
+   *
+   * const tree = BinarySearchTree.from<number>([42, 43, 41]);
+   * ```
+   *
+   * @example Creating a binary search tree from an iterable object
+   * ```ts no-assert
+   * import { BinarySearchTree } from "@std/data-structures";
+   *
+   * const tree = BinarySearchTree.from<number>((function*() {
+   *   yield 42;
+   *   yield 43;
+   *   yield 41;
+   * })());
+   * ```
+   *
+   * @example Creating a binary search tree from an existing binary search tree
+   * ```ts no-assert
+   * import { BinarySearchTree } from "@std/data-structures";
+   *
+   * const tree = BinarySearchTree.from<number>([42, 43, 41]);
+   * const copy = BinarySearchTree.from(tree);
+   * ```
+   *
+   * @example Creating a binary search tree from an array like with a custom comparison function
+   * ```ts no-assert
+   * import { BinarySearchTree, descend } from "@std/data-structures";
+   *
+   * const tree = BinarySearchTree.from<number>(
+   *   [42, 43, 41],
+   *   { compare: descend }
+   * );
+   * ```
+   *
+   * @typeparam T The type of the values stored in the binary search tree.
+   * @param collection An array like, an iterable, or existing binary search tree.
+   * @param options An optional options object to customize the comparison function.
+   * @returns A new binary search tree created from the passed collection.
+   */
+  static override from<T>(
+    collection: ArrayLike<T> | Iterable<T> | StableBinarySearchTree<T>,
+    options?: {
+      compare?: (a: T, b: T) => number;
+    },
+  ): BinarySearchTree<T>;
+  /**
+   * Create a new binary search tree from an array like, an iterable object, or
+   * an existing binary search tree.
+   *
+   * A custom mapping function can be provided to transform the values before
+   * inserting them into the tree.
+   *
+   * A custom comparison function can be provided to sort the values in a
+   * specific order. A custom mapping function can be provided to transform the
+   * values before inserting them into the tree. By default, the values are
+   * sorted in ascending order, unless a {@link BinarySearchTree} is passed, in
+   * which case the comparison function is copied from the input tree. The
+   * comparison operator is used to sort the values in the tree after mapping
+   * the values.
+   *
+   * @example Creating a binary search tree from an array like with a custom mapping function
+   * ```ts no-assert
+   * import { BinarySearchTree } from "@std/data-structures";
+   *
+   * const tree = BinarySearchTree.from<number, string>(
+   *   [42, 43, 41],
+   *   { map: (value) => value.toString() }
+   * );
+   * ```
+   *
+   * @typeparam T The type of the values in the passed collection.
+   * @typeparam U The type of the values stored in the binary search tree.
+   * @typeparam V The type of the `this` value when calling the mapping function. Defaults to `undefined`.
+   * @param collection An array like, an iterable, or existing binary search tree.
+   * @param options The options object to customize the mapping and comparison functions. The `thisArg` property can be used to set the `this` value when calling the mapping function.
+   * @returns A new binary search tree containing the mapped values from the passed collection.
+   */
+  static override from<T, U, V = undefined>(
+    collection: ArrayLike<T> | Iterable<T> | StableBinarySearchTree<T>,
+    options: {
+      compare?: (a: U, b: U) => number;
+      map: (value: T, index: number) => U;
+      thisArg?: V;
+    },
+  ): BinarySearchTree<U>;
+  static override from<T, U, V>(
+    collection: ArrayLike<T> | Iterable<T> | StableBinarySearchTree<T>,
+    options?: {
+      compare?: (a: U, b: U) => number;
+      map?: (value: T, index: number) => U;
+      thisArg?: V;
+    },
+  ): BinarySearchTree<U> {
+    const result = new BinarySearchTree<U>(options?.compare);
+    const stableTree = super.from<T, U, V>(
+      collection,
+      // Cast to use types of `from<T, U, V = undefined>` instead of `from<T>`.
+      // The latter happens by default, even though we call `super.from<T, U, V>`.
+      options as { map: (value: T, index: number) => U },
+    );
+    setRoot(result, getRoot(stableTree));
+    setSize(result, stableTree.size);
+    return result;
+  }
+
+  /**
+   * Finds the node matching the given selection criteria.
+   *
+   * When searching for higher nodes, returns the lowest node that is higher than
+   * the value. When searching for lower nodes, returns the highest node that is
+   * lower than the value.
+   *
+   * By default, only accepts a node exactly matching the passed value and returns
+   * it if found.
+   *
+   * @param value The value to search for
+   * @param select Whether to accept nodes that are higher or lower than the value
+   * @param returnIfFound Whether a node matching the value itself is accepted
+   * @returns The node that matched, or null if none matched
+   */
+  #findNode(
+    value: T,
+    select?: "higher" | "lower",
+    returnIfFound: boolean = true,
+  ): BinarySearchNode<T> | null {
+    const compare = getCompare(this);
+
+    let node: BinarySearchNode<T> | null = getRoot(this);
+    let result: BinarySearchNode<T> | null = null;
+    while (node) {
+      const order = compare(value, node.value);
+      if (order === 0 && returnIfFound) return node;
+
+      let direction: Direction = order < 0 ? "left" : "right";
+      if (select === "higher" && order === 0) {
+        direction = "right";
+      } else if (select === "lower" && order === 0) {
+        direction = "left";
+      }
+
+      if (
+        (select === "higher" && direction === "left") ||
+        (select === "lower" && direction === "right")
+      ) {
+        result = node;
+      }
+
+      node = node[direction];
+    }
+    return result;
+  }
+
+  /**
+   * Finds the lowest (leftmost) value in the binary search tree which is
+   * greater than or equal to the given value, or null if the given value
+   * is higher than all elements of the tree.
+   *
+   * The complexity of this operation depends on the underlying structure of the
+   * tree. Refer to the documentation of the structure itself for more details.
+   *
+   * @example Finding values in the tree
+   * ```ts
+   * import { BinarySearchTree } from "@std/data-structures/unstable-binary-search-tree";
+   * import { assertEquals } from "@std/assert";
+   *
+   * const tree = BinarySearchTree.from<number>([42]);
+   *
+   * assertEquals(tree.ceiling(41), 42);
+   * assertEquals(tree.ceiling(42), 42);
+   * assertEquals(tree.ceiling(43), null);
+   * ```
+   *
+   * @param value The value to search for in the binary search tree.
+   * @returns The ceiling if it was found, or null if not.
+   */
+  ceiling(value: T): T | null {
+    return this.#findNode(value, "higher")?.value ?? null;
+  }
+
+  /**
+   * Finds the highest (rightmost) value in the binary search tree which is
+   * less than or equal to the given value, or null if the given value
+   * is lower than all elements of the tree.
+   *
+   * The complexity of this operation depends on the underlying structure of the
+   * tree. Refer to the documentation of the structure itself for more details.
+   *
+   * @example Finding values in the tree
+   * ```ts
+   * import { BinarySearchTree } from "@std/data-structures/unstable-binary-search-tree";
+   * import { assertEquals } from "@std/assert";
+   *
+   * const tree = BinarySearchTree.from<number>([42]);
+   *
+   * assertEquals(tree.floor(41), null);
+   * assertEquals(tree.floor(42), 42);
+   * assertEquals(tree.floor(43), 42);
+   * ```
+   *
+   * @param value The value to search for in the binary search tree.
+   * @returns The floor if it was found, or null if not.
+   */
+  floor(value: T): T | null {
+    return this.#findNode(value, "lower")?.value ?? null;
+  }
+
+  /**
+   * Finds the lowest (leftmost) value in the binary search tree which is
+   * strictly greater than the given value, or null if the given value
+   * is higher than or equal to all elements of the tree
+   *
+   * The complexity of this operation depends on the underlying structure of the
+   * tree. Refer to the documentation of the structure itself for more details.
+   *
+   * @example Finding values in the tree
+   * ```ts
+   * import { BinarySearchTree } from "@std/data-structures/unstable-binary-search-tree";
+   * import { assertEquals } from "@std/assert";
+   *
+   * const tree = BinarySearchTree.from<number>([42]);
+   *
+   * assertEquals(tree.higher(41), 42);
+   * assertEquals(tree.higher(42), null);
+   * assertEquals(tree.higher(43), null);
+   * ```
+   *
+   * @param value The value to search for in the binary search tree.
+   * @returns The higher value if it was found, or null if not.
+   */
+  higher(value: T): T | null {
+    return this.#findNode(value, "higher", false)?.value ?? null;
+  }
+
+  /**
+   * Finds the highest (rightmost) value in the binary search tree which is
+   * strictly less than the given value, or null if the given value
+   * is lower than or equal to all elements of the tree
+   *
+   * The complexity of this operation depends on the underlying structure of the
+   * tree. Refer to the documentation of the structure itself for more details.
+   *
+   * @example Finding values in the tree
+   * ```ts
+   * import { BinarySearchTree } from "@std/data-structures/unstable-binary-search-tree";
+   * import { assertEquals } from "@std/assert";
+   *
+   * const tree = BinarySearchTree.from<number>([42]);
+   *
+   * assertEquals(tree.lower(41), null);
+   * assertEquals(tree.lower(42), null);
+   * assertEquals(tree.lower(43), 42);
+   * ```
+   *
+   * @param value The value to search for in the binary search tree.
+   * @returns The lower value if it was found, or null if not.
+   */
+  lower(value: T): T | null {
+    return this.#findNode(value, "lower", false)?.value ?? null;
+  }
+}
diff --git a/data_structures/unstable_binary_search_tree_test.ts b/data_structures/unstable_binary_search_tree_test.ts
new file mode 100644
index 000000000000..8e12761a5f1f
--- /dev/null
+++ b/data_structures/unstable_binary_search_tree_test.ts
@@ -0,0 +1,55 @@
+// Copyright 2018-2025 the Deno authors. MIT license.
+import { assertEquals } from "../assert/equals.ts";
+import { BinarySearchTree } from "./unstable_binary_search_tree.ts";
+
+Deno.test("BinarySearchTree.ceiling()", () => {
+  const tree: BinarySearchTree<number> = BinarySearchTree.from(
+    [4, 2, 1, 3, 6, 5, 7],
+  );
+  assertEquals(tree.ceiling(0.5), 1);
+  assertEquals(tree.ceiling(1), 1);
+  assertEquals(tree.ceiling(1.5), 2);
+  assertEquals(tree.ceiling(3.5), 4);
+  assertEquals(tree.ceiling(6.5), 7);
+  assertEquals(tree.ceiling(7), 7);
+  assertEquals(tree.ceiling(7.5), null);
+});
+
+Deno.test("BinarySearchTree.floor()", () => {
+  const tree: BinarySearchTree<number> = BinarySearchTree.from(
+    [4, 2, 1, 3, 6, 5, 7],
+  );
+  assertEquals(tree.floor(0.5), null);
+  assertEquals(tree.floor(1), 1);
+  assertEquals(tree.floor(1.5), 1);
+  assertEquals(tree.floor(4.5), 4);
+  assertEquals(tree.floor(6.5), 6);
+  assertEquals(tree.floor(7), 7);
+  assertEquals(tree.floor(7.5), 7);
+});
+
+Deno.test("BinarySearchTree.higher()", () => {
+  const tree: BinarySearchTree<number> = BinarySearchTree.from(
+    [4, 2, 1, 3, 6, 5, 7],
+  );
+  assertEquals(tree.higher(0.5), 1);
+  assertEquals(tree.higher(1), 2);
+  assertEquals(tree.higher(1.5), 2);
+  assertEquals(tree.higher(3.5), 4);
+  assertEquals(tree.higher(6.5), 7);
+  assertEquals(tree.higher(7), null);
+  assertEquals(tree.higher(7.5), null);
+});
+
+Deno.test("BinarySearchTree.lower()", () => {
+  const tree: BinarySearchTree<number> = BinarySearchTree.from(
+    [4, 2, 1, 3, 6, 5, 7],
+  );
+  assertEquals(tree.lower(0.5), null);
+  assertEquals(tree.lower(1), null);
+  assertEquals(tree.lower(1.5), 1);
+  assertEquals(tree.lower(4.5), 4);
+  assertEquals(tree.lower(6.5), 6);
+  assertEquals(tree.lower(7), 6);
+  assertEquals(tree.lower(7.5), 7);
+});