diff --git a/lib/bst.js b/lib/bst.js
index 2276f67..98bcb16 100644
--- a/lib/bst.js
+++ b/lib/bst.js
@@ -328,16 +328,6 @@ BinarySearchTree.prototype.getUpperBoundMatcher = function (query) {
 };
 
 
-// Append all elements in toAppend to array
-function append (array, toAppend) {
-  var i;
-
-  for (i = 0; i < toAppend.length; i += 1) {
-    array.push(toAppend[i]);
-  }
-}
-
-
 /**
  * Get all data for a key between bounds
  * Return it in key order
@@ -352,9 +342,9 @@ BinarySearchTree.prototype.betweenBounds = function (query, lbm, ubm) {
   lbm = lbm || this.getLowerBoundMatcher(query);
   ubm = ubm || this.getUpperBoundMatcher(query);
 
-  if (lbm(this.key) && this.left) { append(res, this.left.betweenBounds(query, lbm, ubm)); }
-  if (lbm(this.key) && ubm(this.key)) { append(res, this.data); }
-  if (ubm(this.key) && this.right) { append(res, this.right.betweenBounds(query, lbm, ubm)); }
+  if (lbm(this.key) && this.left) { res = res.concat(this.left.betweenBounds(query, lbm, ubm)); }
+  if (lbm(this.key) && ubm(this.key)) { res = res.concat(this.data); }
+  if (ubm(this.key) && this.right) { res = res.concat(this.right.betweenBounds(query, lbm, ubm)); }
 
   return res;
 };