CODE EXAMPLE FOR HTML

html select subselect

<select>
  <optgroup label="Options 1">
     <option>Option 1.1</option>
     <option>Option 1.2</option>
  </optgroup>
  <optgroup label="Options 2">
     <option>Option 2.1</option>
     <option>Option 2.2</option>
  </optgroup>
</select>