怎么算树的深度？

func getdep(t:bittree):integer;
{t指向根接点}
if t=nil return(0);
else
return(max(getdep(t.lchind),getdep(t.rchild))+1)
endf;{getdep}
请问如何以此例理解递归深度和递归数的含义。请指教 --------------------   Optimistic is my color
　 We spend our time on something from dawn to dark
   Day in and day out
　 Sun rise and down　
　 Make an own goal to confront life　
   Self-discovery is the first step toward self-appreciation
   成功只会降临在自认为会成功的人身上