<select class="select2-icon" name="icon">
    <option value="fa-user" data-icon="fa-user">user</option>
    <option value="fa-user-circle" data-icon="fa-user-circle">user-circle</option>
    <option value="fa-user-tie" data-icon="fa-user-tie">user-tie</option>
    <option value="fa-user-secret" data-icon="fa-user-secret">user-secret</option>
    <option value="fa-user-ninja" data-icon="fa-user-ninja">user-ninja</option>
</select>


<script>
  function formatText (icon) {
      return $('<span><i class="fas ' + $(icon.element).data('icon') + '"></i> ' + icon.text + '</span>');
  };
  $('.select2-icon').select2({
      width: "50%",
      templateSelection: formatText,
      templateResult: formatText
  });
</script>