You can create templates for multi-level Drupal menus. Before you try this, you should follow the guide for creating a simple single level menu as this explains the full process.

Structuring a multi-level menu

The screen-shot below shows the structure of a 3 level menu template. It shows that for each level required in the menu, you must add a new Menu list container, Menu list item and Menu link. These must be nested within the Menu list item of the parent level.

If you require more than three levels, simply nest additional elements in the same pattern below. You can nest as many levels as you want. Any nested elements not required by your menu are simply ignored.