notes/_includes/nav.html

<ul class="nav-list">
  {%- assign ordered_pages_list = site.html_pages | where_exp:"item", "item.nav_order != nil" -%}
  {%- assign unordered_pages_list = site.html_pages | where_exp:"item", "item.nav_order == nil" -%}
  {%- if site.nav_sort == 'case_insensitive' -%}
    {%- assign sorted_ordered_pages_list = ordered_pages_list | sort_natural:"nav_order" -%}
    {%- assign sorted_unordered_pages_list = unordered_pages_list | sort_natural:"title" -%}
  {%- else -%}
    {%- assign sorted_ordered_pages_list = ordered_pages_list | sort:"nav_order" -%}
    {%- assign sorted_unordered_pages_list = unordered_pages_list | sort:"title" -%}
  {%- endif -%}
  {%- assign pages_list = sorted_ordered_pages_list | concat: sorted_unordered_pages_list -%}
  {%- for node in pages_list -%}
    {%- unless node.nav_exclude -%}
      {%- if node.parent == nil and node.title -%}
        <li class="nav-list-item{% if page.url == node.url or page.parent == node.title or page.grand_parent == node.title %} active{% endif %}">
          {%- if page.parent == node.title or page.grand_parent == node.title -%}
            {%- assign first_level_url = node.url | absolute_url -%}
          {%- endif -%}
          {%- if node.has_children -%}
            <a href="#" class="nav-list-expander"><svg viewBox="0 0 24 24"><use xlink:href="#svg-arrow-right"></use></svg></a>
          {%- endif -%}
          <a href="{{ node.url | absolute_url }}" class="nav-list-link{% if page.url == node.url %} active{% endif %}">{{ node.title }}</a>
          {%- if node.has_children -%}
            {%- assign children_list = pages_list | where: "parent", node.title -%}
            <ul class="nav-list ">
            {%- for child in children_list -%}
              {%- unless child.nav_exclude -%}
                <li class="nav-list-item {% if page.url == child.url or page.parent == child.title %} active{% endif %}">
                  {%- if page.url == child.url or page.parent == child.title -%}
                    {%- assign second_level_url = child.url | absolute_url -%}
                  {%- endif -%}
                  {%- if child.has_children -%}
                    <a href="#" class="nav-list-expander"><svg viewBox="0 0 24 24"><use xlink:href="#svg-arrow-right"></use></svg></a>
                  {%- endif -%}
                  <a href="{{ child.url | absolute_url }}" class="nav-list-link{% if page.url == child.url %} active{% endif %}">{{ child.title }}</a>
                  {%- if child.has_children -%}
                    {%- assign grand_children_list = pages_list | where: "parent", child.title | where: "grand_parent", node.title -%}
                    <ul class="nav-list">
                    {%- for grand_child in grand_children_list -%}
                      <li class="nav-list-item {% if page.url == grand_child.url %} active{% endif %}">
                        <a href="{{ grand_child.url | absolute_url }}" class="nav-list-link{% if page.url == grand_child.url %} active{% endif %}">{{ grand_child.title }}</a>
                      </li>
                    {%- endfor -%}
                    </ul>
                  {%- endif -%}
                </li>
              {%- endunless -%}
            {%- endfor -%}
            </ul>
          {%- endif -%}
        </li>
      {%- endif -%}
    {%- endunless -%}
  {%- endfor -%}
</ul>