Multi-level sorting

Hello,
I've a data tree with unlimited depth level rendered with ul-li-ul-...
markup (using jquery.treeview). I want to allow node sorting, but only
within the parent node, i.e.
1
1.1
1.2
1.3
1.3.1
2
3
3.1
and you can sort only 1-2-3 or 1.1-1.2-1.3 etc.
How should I setup the sortables calls?