quill/docs/_includes/sidebar.html

{% for parent in include.items %}
<li{% if page.url contains parent.url %} class="active"{% endif %}>
  <a href="{{ parent.url }}">{{ parent.title }}</a>
  {% if parent.children != null %}
  <ul>
    {% for child in parent.children %}
    <li{% if page.url contains child.url %} class="active"{% endif %}>
      <a href="{{ child.url }}">{{ child.title }}</a>
    </li>
    {% endfor %}
  </ul>
  {% endif %}
</li>
{% endfor %}