Hi Dennis,
Thanks for using Syncfusion products
With regard to your query, the tree view node images can be customized with CustomCss property and by overriding the whole css with the 8.104.0.30 version
TreeViewModel model = new TreeViewModel();
model.CustomCSS = "MyTreeViewStyle";
and define the css. You can download the css from the below location
http://help.syncfusion.com/support/Tools_MVC/Forums/95197/TreeView.cssLet me know if you have any queries
Best Regards,
Premkumar D