navigation menu

Hello I found this good article to formatting custom menu
https://digwp.com/2011/11/html-formatting-custom-menus/
but menu have depth 0

<ul>
<li>menu 1</li>
<li>menu 2</li>
<li>menu 3</li>
</ul>

I need to format like wp menu saving area like

<ul>
<li>menu 1
<ul>
<li>sub menu 1-1</li>
<li>sub menu 1-2</li>
</ul>
</li>
<li>menu 2</li>
<li>menu 3</li>
</ul>