It this issue related? https://forum.mendix.com/questions/3653/Enums-image-on-tree-view
You can file an issue on Github. The problem with the TreeViewAndGridView widget is that it is not actively supported, because the code is very, very old. We might look into it (if there is time), if the Community has a suggestion and/or pull request on Github regarding this issue, it is most welcome.