lib.itmens/common/templates/widgets/multi_select.html

<select name="{{ widget.name }}"
        {% include "django/forms/widgets/attrs.html" %}>
  {% for group_name, group_choices, group_index in widget.optgroups %}
    {% if group_name %}<optgroup label="{{ group_name }}">{% endif %}
      {% for option in group_choices %}
        {% include option.template_name with widget=option %}
      {% endfor %}
      {% if group_name %}</optgroup>{% endif %}
  {% endfor %}
</select>
<script>
    $('select[name="{{ widget.name }}"]').multipleSelect({
        selectAll: false,
        width: "100%",
        displayTitle: true,
        // any value greater than number of genres
        minimumCountSelected: 50,
        filter: true,
    })
</script>