title: ItemsControl where entire item is expander for sub-items
body: <p>So it's kind of hard to describe the behavior I want, so I drew a nice picture with my amateur paint skills.</p>
  
  <p><img src="https://i.stack.imgur.com/xY0c6.png" alt="enter image description here"></p>
  
  <p>So basically I want the headings of the <code>ItemsControl</code> to operate like an expander, without the ugly expander icon that comes along (so just clicking anywhere in the box would expand to see the sub items).  I already have the data-hierarchy in place, but I cannot for the life of me get the expander to behave as I want, anybody had any success overriding expander styles to accomplish something like this, or is there another control that can accomplish something like this easier?  Here's some simple code, but has the ugly expander button, overriding the headertemplate and style of the expander has only made it look much worse.</p>
  
  <pre><code>&lt;ItemsControl ItemsSource="{Binding Collection}" 
    HorizontalContentAlignment="Stretch"&gt;
      &lt;ItemsControl.ItemTemplate&gt;
          &lt;DataTemplate&gt;
              &lt;Expander Header="Heading"&gt;
                  &lt;ItemsControl ItemsSource="{Binding Items}" HorizontalContentAlignment="Stretch"&gt;
                      &lt;ItemsControl.ItemTemplate&gt;
                          &lt;DataTemplate&gt;
                              &lt;Expander Header="Sub-Heading"&gt;
                                  &lt;ListBox ItemsSource="{Binding Items}" HorizontalContentAlignment="Stretch"/&gt;
                              &lt;/Expander&gt;
                          &lt;/DataTemplate&gt;
                      &lt;/ItemsControl.ItemTemplate&gt;
                  &lt;/ItemsControl&gt;
              &lt;/Expander&gt;
          &lt;/DataTemplate&gt;
      &lt;/ItemsControl.ItemTemplate&gt;
  &lt;/ItemsControl&gt;
  </code></pre>