public function handle($request, Closure $next)
{
    Menu::make('NavBar', function($menu){
        $menuitems = MenuItem::all();
        foreach($menuitems as $menuitem)
        {
            if(!is_null($menuitem->parent)){
               // For example, 'Conferences', a top level menu item with a null parent field
               $menu->add($menuitem->title, url($menuitem->url));
            }
            else{
                // Parent is a field in database, for example 'Traverse City 2015' would have the parent 'conferences'
                $parent = $menuitem->parent;
                $menu->item('about')->add($menuitem->title, url($menuitem->url));

            }
        }
    });
    return $next($request);
}

{!! $NavBar->asUl() !!}

<ul>
  <li><a href="/conferences">Conferences</a></li>
  <ul>
    <li><a href="/conferences/traverse-city-2015">Traverse City 2015</li>
  </ul>
</ul>

<ul>
  <li><a href="/conferences/">Conferences</a></li>
  <li><a href="/conferences/traverse-city-2015">Traverse City 2015</a></li>
</ul>