title: How to add property to class without overriding?
body: <p>I am trying to extend the TreeViewItem to add a property. What complicates it is that it has an "Items" property that is a list of the same class type. Adding a property will require me override the children property which I do not want to do. Here is the original TreeViewItem:</p>
  
  <pre><code>public class TreeViewItem : NavigationItem&lt;TreeViewItem&gt;, INavigationItemContainer&lt;TreeViewItem&gt;, ITreeViewItem
  {
      public IList&lt;TreeViewItem&gt; Items { get; }
  }
  </code></pre>
  
  <p>How do I add MyProperty without being forced to override the "Items" property. A lot of things happen with the "Items" property that I do not want to recreate. Thanks for any help or advice.</p>