In order to use the drag and drop
functionality in treeview, you can simply set the RadTreeView with EnableDragAndDrop="True"
and you will be able to drag and drop
Also RadTreeView supports its own context menus- Demo
Now, if you want to move the nodes using the contextmenu (ie, right-clicking a node and selecting 'Move node' and then right clicking another node and selecting 'Drop here'), then one suggestion is,
event, remove the node from the source node collection and then add create a new instance of node and then add the node in the dropped node collection (according to menuitm clicked). You can refer the following demo which will help you in adding and removing the nodes.
Hopes this suggestion helps,