It is not clear what you want to drop on your treeview's node. But for the simple case of dragging another node from the treeview itself, the attached (incomplete) project shows one way to go about this.
It is incomplete because no action is taken when the node is dropped, and because the Accept parameter is simply set to True unless you try to drop a node on itself. A real app would obviously have a customised algorithm for this so only acceptable nodes were highlighted.