I have a list of a class looking something like this:

Code:
class MyClass
{
   string Group {get;set;}
   string SubGroup {get;set;}
   string Item {get;set;}
}
In my treeview I want the list to be grouped like:

Group1
...SubGroup1
......Item1
......Item 2
...SubGroup2
......Item3
...SubGroup3
......Item4
......Item5
Group2
...SubGroup4
......Item6

What should my xaml look like for that?

I've experimented with nested HierarchicalDataTemplates and a CollectionViewSource, but nothing seemed to really work....