Add the option to show the process tree from a single process id.

[smithandrewl]

This would show the graph of processes created (directly or indirectly) by the process id passed in as a script parameter.

Running the script with no arguments would produce the output it produces now
Running the script with a numeric argument would produce the tree of child processes for that process.

[cfletemier]

Looks like fun. Mind assigning this to me?

[smithandrewl]

Sounds great, it is yours. Fork the repo and then send me a pull request when you have finished in your fork.