{% set values_amount = values|length %}
{% set selected_values = current_values|split(',') %}
<select class="resize-vertical" size="{{ values_amount < 10 ? values_amount : 10 }}" multiple>
  {% for value in values %}
    <option value="{{ value|raw }}"{{ value in selected_values ? ' selected' }}>{{ value|raw }}</option>
  {% endfor %}
</select>