I've been trying to loop a collection nested. Their parent and child, but haven't been successful so far.

      {{ collection:navigation scope="item" section:is="Main" parent:doesnt_exist="true" }}
      <li class="nav-item">
        <a href="{{ item:landing_url }}" target="{{ item:target }}">{{ title }}</a>
      </li>

      {{ collection from="navigation" scope="item" parent:is="{item:id}" }}
      <a href="#">{{ title }}</a>
      {{ /collection }}

      {{ /collection:navigation }}

The code I've been using is shown above. It displays the parents, but not the child. If I pass a static value to parent:is, It seems to work.