Add ability to the Tree to have a different icon per node. This way, a developer could change the icon for a node depending on their needs. An example where this would be useful is if you are using the tree to allow the user to build and publish a book. If a page in the book is not published you might want to have a custom graphic that reflects that the page is not published, which is different than the default graphic for a node. In this scenario, the default graphic would still be needed for published pages.