wp_nav_menu

Hi there, please help me before I loose my mind.

I want to separate the UL’s in the response from wp_nav_menu(). But I can’t for my life figure out how. Like this:

echo #1:
<ul>
      <li class='active'>Top Menu Item 1</li>
      <li>Top Menu Item 2</li>
      etc
</ul>

echo #2:
<ul> // Submenu of Top Menu Item 1
      <li class='active'>Sub Menu Item 1</li>
      <li>Sub Menu Item 2</li>
      etc
</ul>