<select>
  <optgroup label="South America">
    <option>Uruguay</option>
    <option>Brazil</option>
    <option>Argentina</option>
  </optgroup>
  <optgroup label="Europe">
    <option>Italy</option>
    <option>Germany</option>
    <option>England</option>
    <option>France</option>
    <option>Spain</option>
  </optgroup>
</select>

<select>
  <optgroup label="Winter">
    <option>December</option>
    <option>January</option>
    <option>February</option>
    <option>March</option>
  </optgroup>
  <optgroup label="Not winter" disabled>
    <option>April</option>
    <option>May</option>
    <option>June</option>
    <option>July</option>
    <option>August</option>
    <option>September</option>
    <option>October</option>
    <option>November</option>
  </optgroup>
</select>