how to create a submenu in ghost cms
{{#if isSecondary}}
<ul class="nav" role="menu">
{{#foreach navigation}}
<li class="nav-{{slug}}" role="menuitem">
<a href="{{url}}">
<svg class="icon" role="img" aria-label="{{slug}} icon">
<title>{{slug}}</title>
<use xlink:href="#{{slug}}"></use>
</svg>
</a>
</li>
{{/foreach}}
</ul>
{{else}}
<ul class="nav" role="menu">
{{#foreach navigation}}
<li class="{{link_class for=(url) class=(concat "nav-" slug)}}" role="menuitem">
<a href="{{url absolute="true"}}">{{label}}</a>
</li>
{{/foreach}}
</ul>
{{/if}}