title: Checkable MenuItem With Sub Menus
body: <p>Can you have submenus with the top level set to checkable in WPF?  I can't seem to get this to work.</p>
  
  <p></p>
  
  <pre><code>&lt;Window.ContextMenu&gt;
      &lt;ContextMenu&gt;
          &lt;MenuItem Header="Top Level 1" IsCheckable="True" IsChecked="True"&gt;
              &lt;MenuItem Header="Sub Level" /&gt;
              &lt;MenuItem Header="Sub Level" /&gt;
          &lt;/MenuItem&gt;
          &lt;MenuItem Header="Top Level 2"&gt;
              &lt;MenuItem Header="Sub Level" /&gt;
              &lt;MenuItem Header="Sub Level" /&gt;
          &lt;/MenuItem&gt;
      &lt;/ContextMenu&gt;
  &lt;/Window.ContextMenu&gt;
  </code></pre>
  
  <p></p>
  
  <p>Top Level 1 is checkable, but the sub levels don't appear.  Any thoughts?</p>