Unluckly the core of the Mvc Controls Toolkit use Validation classes introduced with ,Net 4.0. Moreover it uses also optional parameter specified by name, so it is hard to mofify it to run in 3.5.
However it runs also with MVC 2 (there are two versions of the library one for MVC3 and the other for Mvc 2).
other treeviews that allow this.
For display only purposes you can use the jquery treeview: http://docs.jquery.com/Plugins/Treeview