ASP net - Navigation w/ 2nd & 3rd Level in Popout

[HTMLBasicTutor]

I can do this manually c/w popping out, lists and CSS but now I want to convert this to work with ASP.net.

Level1 is a list down the left.

Level 2 and 3 are in the popout.

Corresponding Level 3 is under it's Level 2 category.

See attached image. Probably easier to see than describe in words.

Could someone please provide some coding samples on how to do this. Tutorials would help also.