title: How to bind a Treeview's SelectedItem via DataSource to a Datagrid
body: <p>I would need to bind selected treeview item (actually datasource of that) to datagrid.</p>
  
  <p>F.ex. I have list of receipts, and under one receipt there is list of receipt-items. I would like to bind those items to datagrid when receipt is selected from treeview.</p>
  
  <p>In datagrid receipt-items would be edited, so values should be bind to actual datasource.</p>
  
  <p>How to do this?</p>