Comments by Evgeny Bestfator (Top 1 by date)

Reason for my vote of 3 \n Капитан очевидность)) Склеил тривью и контент контрол и рад.

You could have same effect with just using XAML and without writing any control:

<grid>
<grid.columndefinition>
<grid.columndefinition>
<treeview x:name="tv">
<contentcontrol grid.column="1" content="{Binding Source={RelativeSource ElementName=" tv"},="" path="SelectedItem.Tag}"">