Hello,
Thank you for your post. I have been looking into and I created a sample project for you with the functionality you want. Basically I set the XamDataTrees’ AllowDragDropCopy Property to true, which means that you hold “Ctrl” key while dragging, the DragDropEventArgs’ OperationType is Copy and you can implement copying of the Node instead the built in Move operation. Also you should drop the Node over another Node, not between two Nodes. Please let me know if this helps you or you need further assistance on this matter.
Looking forward for your reply.