Perhaps a good way to go about that would be:
- Handle the NodeDrop event of the TreeView that is a drop-target on the server. Add the node to the same tree, clone it and add the clone to the mirror-treeView.
You can use the AjaxManager to update all the TreeViews (they all should be updated), or if easier - place the TreeViews in the same AjaxPanel.
Please, let me know if you this somehow doesn't work for this case or having troubles implementing it! I am happy to help!
the Telerik team