drupal function theming for custom menu

i have a custom menu with three levels. It is in format:

- a/b1/c1   - a/b2/c2   - a/b3/c3

I want to have same css formatting for all the b1, b2, b3 and same formatting in c1,c2,c3 but different between them. I have found that the function that renders that menu is: theme_开发者_开发问答menu_item_link() But the same function renders the b1 and c1 too. Is there a way to separate them in templates.php and have them format them differently. Is there any other way around. Thank u in advance people

You might want to take a look at nice menus if you want to make a tree like menu structure.