title: WPF: TreeView - conditional placement of button to expand subitems
body: <p>I would like to build a TreeView with the following features:</p>
  
  <ol>
  <li>The first level should have the expander-button not on the left but on the right side</li>
  <li>All sublevels should have the expander-button on the left - just like the default TreeViewItem</li>
  <li>Expanding/Collapsing should be animated just like the expander-control</li>
  </ol>
  
  <p>I was messing around with DataTemplate and HierarchicalDataTemplate, but the Expander-Button does not seem to be part of the Template, its always added to the Template and always on the left side.
  How can I place the Expander-Button depending on the item-level?</p>