Hi Dharmesh,
getNavigation sub tree can get for you 10 levels in advance.
check the detrails, 4th parameters is number of levels (limited by 10):
getNavigationSubTree = function(name, callback, argument, levels)
If you have max 10 levels this will suit your needs.
As for your code, best would be just to debug it with chrome js debugger and see why is it finding only one node.
Best Regards,
Tal