Unable to Understand with dryrun with stack

#1

Can u please explain how this code actually work in stack memory. With particular value of n and fxn call.

#2

see this for n==5 fib(5) will expnd like this:

                          fib(5)   
                     /                \
               fib(4)                fib(3)   
             /        \              /       \ 
         fib(3)      fib(2)         fib(2)   fib(1)
        /    \       /    \        /      \
  fib(2)   fib(1)  fib(1) fib(0) fib(1) fib(0)
  /     \
fib(1) fib(0)