title: Windows Form - How add header not selectable in combobox item in C#?
body: <p>I need create a custom combobox control that allows header as separator which should not be selectable using the mouse move or key press. </p>
  
  <p>this is example:</p>
  
  <pre><code>Header1
    item1
    item2
    item3
  Header2
    item4
    item5
  </code></pre>
  
  <p>I tried many solutions, without success. Thanks in advance!</p>