How can I only change children order in the nested example

[beshoo]

Dear all.
I am looking to use a nested example.
I want to be able to only change the children's order, so I want to disable the movement of any child to another parent and or moving the child to be a child of the previous child and I want to disable moving a parent to be a child to another parent or child.

[festo]

@beshoo Check this example, this helped me: https://jsbin.com/xihicevama/1/edit?html,css,js,output