{assign var='ul1' value=$ul1|default:'nav'}
{assign var='ul2' value=$ul2|default:$ul1}
{assign var='ul3' value=$ul3|default:$ul2}

{foreach from=$index item=page}
  <ul>
  {foreach from=$page.children item=page}
      {navItem page=$page active=$id}
  {/foreach}
  </ul>
{/foreach}