mkdocs-material/material/nav.html

{% if nav_item.children %}
  <li>
    <span class="section">{{ nav_item.title }}</span>
    <ul>
      {% for nav_item in nav_item.children %}
        {% include "nav.html" %}
      {% endfor %}
    </ul>
  </li>
{% else %}
  <li>
    <a class="{% if nav_item.active %}current{% endif %}" title="{{ nav_item.title }}" href="{{ nav_item.url }}">
      {{ nav_item.title }}
    </a>
    {% if nav_item == current_page %}
      {% if h1 %}
        {% set toc = (toc | first).children %}
      {% endif %}
      {% if toc %}
        <ul>
          {% for toc_item in toc %}
            <li class="anchor">
              <a title="{{ toc_item.title }}" href="{{ toc_item.url }}">
                {{ toc_item.title }}
              </a>
            </li>
          {% endfor %}
        </ul>
      {% endif %}
    {% endif %}
  </li>
{% endif %}