I have a source with ~270 items which I want to display in treeview and rendering of this list takes 1-2min. This is very slow, and I believe that using a virtualization should take care of that but it seems not. Also, I see same performance either with IsVirtualizing="True" or "False". As you can see, I also put additional properties, but without success. Another observation is that once items are displayed, there is additional time before UI unfreeze.
This is xaml for treeview.