title: SelectList with tiered optgroups?
body: <p>I did some searching but wasn't able to find a post that matched what I was looking for.</p>
  
  <p>I currently have a <code>SelectList</code> with the following structure:</p>
  
  <p>Code:</p>
  
  <pre><code>&lt;optgroup1&gt;
     &lt;Question1&gt;
     &lt;Question2&gt;
     &lt;Question3&gt;
     &lt;Question4&gt;
  &lt;optgroup1&gt;
  &lt;optgroup2&gt;
     &lt;Question1&gt;
     &lt;Question2&gt;
     &lt;Question3&gt;
     &lt;Question4&gt;
  &lt;optgroup2&gt;
  </code></pre>
  
  <p>Now, I am trying to split the questions into optgroups of their own so that the format is more like this:</p>
  
  <p>Code 2:</p>
  
  <pre><code>&lt;optgroup1&gt;
      &lt;subgroup1&gt;
         &lt;Question1&gt;
         &lt;Question2&gt;
      &lt;subgroup1&gt;
      &lt;subgroup2&gt;
         &lt;Question3&gt;
         &lt;Question4&gt;
      &lt;subgroup2&gt;
  &lt;optgroup1&gt;
  &lt;optgroup2&gt;
     &lt;subgroup3&gt;
         &lt;Question1&gt;
         &lt;Question2&gt;
     &lt;subgroup3&gt;
     &lt;subgroup4&gt;
         &lt;Question3&gt;
         &lt;Question4&gt;
     &lt;subgroup4&gt;
  &lt;optgroup2&gt;
  </code></pre>
  
  <p>Is it possible to create a tiered <code>SelectList</code> like <em>Code 2</em>? The trouble I'm running into is that when I create the list of questions as <code>SelectListItems</code>, I set the <code>Text</code>, <code>Value</code>, and the <code>Group</code> as a <code>SelectListGroup</code>. This is working to create a <code>SelectList</code> like the one in my first example, but I am having difficult wrapping my head around/knowing if it's possible to use multiple tiered <code>SelectListGroups</code> and how to approach this.</p>