I'm trying to make a selectable option's tree like this:
<select>
  <optgroup label="Category 1">
    <option>Sub Category 1</option>
    <option>Sub Category 2</option>
  </optgroup> 
  <optgroup label="Category 2">
    <option>Sub Category 3</option>
    <option>Sub Category 4</option>
  </optgroup>
  <optgroup label="Group 3" disabled>
  </optgroup>
</select>
but, as you can see, i'm not able to select the main categories because they're just simple labels.
I've been looking for a different solution but unfortunally i didn't find nothing yet.