<!-- required files -->
<link href="../assets/plugins/select2/dist/css/select2.min.css" rel="stylesheet" />
<script src="../assets/plugins/select2/dist/js/select2.min.js"></script>

<!-- html -->
<select class="default-select2 form-control">
  <optgroup label="Alaskan/Hawaiian Time Zone">
    <option value="AK">Alaska</option>
    <option value="HI">Hawaii</option>
  </optgroup>
</select>

<!-- multiple selection -->
<select class="multiple-select2 form-control" multiple>
  ...
</select>

<!-- script -->
<script>
  $(".default-select2").select2();
  $(".multiple-select2").select2({ placeholder: "Select a state" });
</script>