title: How to add subitems dynamically to a TMenuItem the moment its subitems are shown
body: <p>I have a menu structure like this:</p>
  
  <pre><code>1. Option A
      1.1 Option B
          1.1.1 Option C
          1.1.2 Option D
      1.2 Option C
          1.2.1 Option B
          1.2.2 Option D
      1.3 Option D
          1.3.1 Option B
          1.3.2 Option C
  2. Option B
      2.1 Option A
          2.1.1 Option C
          2.1.2 Option D
      2.2 Option C
          2.2.1 Option A
          2.2.2 Option D
      2.3 Option D
          2.3.1 Option A
          2.3.2 Option C
  3. Option C
      3.1 Option A
          3.1.1 Option B
          3.1.2 Option D
      3.2 Option B
          3.2.1 Option A
          3.2.2 Option D
      1.3 Option D
          3.3.1 Option A
          3.3.2 Option B
  4. Option D
      4.1 Option A
          4.1.1 Option B
          4.1.2 Option C
      4.2 Option B
          4.2.1 Option A
          4.2.2 Option C
      4.3 Option C
          4.3.1 Option A
          4.3.2 Option B
  </code></pre>
  
  <p>Why do I do such thing? - This menu is used to select a combination of options <code>A,B,C,D</code> where sequence of selected options matters.<br>
  For Example: The user clicks on menu-item 2.3.1. That results in combination <code>B-D-A</code>.</p>
  
  <p>Now, you know how I currently do it theoretically. Actually, there are much more options to combine. But only three are to be combined at the same time.<br>
  <strong>The problem is</strong> that I have to create all menu-items (three levels deep) before the menu is shown.</p>
  
  <p>Is there a way to add submenu-items just when they are needed (that is when they should be shown)?</p>