<div class="form-group">
    <label>Acciones</label>
    <select class="form-control select2" id="idAcciones" name="accionesID" style="width: 100%;" required>
        {% for accion in acciones  %}
            <option value="{{ accion.accionID }}">{{ accion.accionTITULO }}</option>
        {% endfor %}   
    </select>
</div>

<script type="text/javascript">
    $(document).ready(function() {
        $('.select2').select2();
    });
</script>