Ive got this function, but it didnt worked well for me and i hope you guys can help me:
Edit fiddle - JSFiddle

How can i change the function, that when I click on a "level_1" "li", the child ul "level_2" nav gets "visablity:visible", the div with the id "nav" gets the height of the child ul "level_2"and slides down. When I click on another "level_1" li, the div "nav" goes up again and the child "level_2" ul gets "visabilty:hidden" again.