Your program should accept an argument from commmand line which denotes
the level of your fully binary tree.
With input 1, only a process is created. (no fork() needed in this case).
With input 2, 3 processes is created.
With input 3, 7 processes is created.
Each process will print its pid and its ppid.
And the messages of processes are printed in PRE-order.
Example:
$ ./proctree 1
pid=25972, ppid=25870
$ ./proctree 2
pid=25975, ppid=25870
pid=25976, ppid=25975
pid=25979, ppid=25975
$ ./proctree 3 (The pid of the shell is 25870.)
pid=25982, ppid=25870
pid=25983, ppid=25982
pid=25984, ppid=25983
pid=25987, ppid=25983
pid=25990, ppid=25982
pid=25991, ppid=25990
pid=25994, ppid=25990
$