This week's book giveaway is in the OCAJP 8 forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide and have Edward Finegan & Robert Liguori on-line! See this thread for details.
Make your tree editable, but use a custom TreeCellEditor to prevent leaf cells from being edited. I think pretty much all you'd have to do is extend DefaultTreeCellEditor, and in the getTreeCellEditorComponent() method just call setEditable( !leaf ).
Write once, run anywhere, because there's nowhere to hide! - /. A.C.