{% if site.data.navigation.items.size > 0 %}
    {% for item in site.data.navigation.items %}
  • {{ item.title }} {% if item.subitems.size > 0 %}
      {% for sitem in item.subitems %}
    • {{ sitem.title }}
    • {% endfor %}
    {% endif %}
  • {% endfor %}
{% else %}
  • NOTICE: There're no items. You can add them on _data/navigation.
{% endif %}