DragDrop in TreeView- knowing where the drag came from

Question

I have two TreeView objects and I am able to do drag and drop operations between them- I've defined all the functions- dragenter, dragdrop, etc. What I want to do is be able to tell within the dragdrop function whether or not the item being dragged came from that TreeView or the other one. This would be easy if I had a reference to the other TreeView object- but even the dragenter function's sender is the current TreeView, not the one it entered from. And the info being passed is just being passed as a ResourceInfo embedded as a DataObject in the eventargs. Any ideas? -David