title: How to create borders on TreeViewItems?
body: <p>I have a TreeView that uses a Hierarchical Data Template.</p>
  
  <p>I want to create borders around the Parent Elements with borders on the child elements. </p>
  
  <p>So it might look something like:</p>
  
  <pre><code>----------------------------------------
  |                                      |
  |                Big Border            |
  |    |-----------Child Border---- --|  |
  |    |------------------------------|  |
  |                                      |     
  |                                      |
  ----------------------------------------
  </code></pre>
  
  <p>This is XAML so far:</p>
  
  <pre><code>&lt;Window.Resources&gt;
      &lt;Style x:Key="TreeViewStyle" TargetType="TreeViewItem"&gt;
          &lt;Setter Property="Margin" Value="0, 10, 0, 0"/&gt;
      &lt;/Style&gt;
      &lt;Style x:Key="PitcherStyling" TargetType="TextBlock"&gt;
          &lt;Style.Triggers&gt;
              &lt;DataTrigger Binding="{Binding IsAce}" Value="True"&gt;
                  &lt;Setter Property="FontWeight" Value="Bold"/&gt;
              &lt;/DataTrigger&gt;
          &lt;/Style.Triggers&gt;
      &lt;/Style&gt;
  &lt;/Window.Resources&gt;
  &lt;Grid&gt;
      &lt;TreeView ItemsSource="{Binding Team.Players}" ItemContainerStyle="{StaticResource TreeViewStyle}"&gt;
          &lt;TreeView.Resources&gt;
              &lt;HierarchicalDataTemplate DataType="{x:Type local:LongRelief}" ItemsSource="{Binding Path=Attributes}"&gt;
                  &lt;StackPanel Orientation="Horizontal"&gt;
                          &lt;TextBlock Text="{Binding Name}"/&gt;
                          &lt;TextBlock Text="{Binding Max Innings}" Style="{StaticResource GroupTypeStyling}"/&gt;
                      &lt;/StackPanel&gt;
              &lt;/HierarchicalDataTemplate&gt;
              &lt;HierarchicalDataTemplate DataType="{x:Type local:StartingPitcher}" ItemsSource="{Binding Path=Attributes}"&gt;
                  &lt;StackPanel Orientation="Horizontal"&gt;
                          &lt;TextBlock Text="{Binding Name}"/&gt;
                          &lt;TextBlock Text="{Binding Strikeout Pitch}" Style="{StaticResource PitcherStyling}"/&gt;
                      &lt;/StackPanel&gt;
              &lt;/HierarchicalDataTemplate&gt;
          &lt;/TreeView.Resources&gt;
      &lt;/TreeView&gt;
  &lt;/Grid&gt;
  </code></pre>
  
  <p>So, the Parent Elements will be Starting Pitcher and Long Relief Pitchers will always be children of Starting Pitcher. </p>
  
  <p>So I would want a border that acts as a container for a Starting Pitcher and all of the Long Relief Pitcher Children and for each of these Long Relief Children, they have their own mini border.</p>