[littleq0903]

This might be kind of off-topic, but I am interested in how he create this tree diagram, is there any tool could do that? or just handmade?

[amenghra]

A fun tool once you have handmade diagrams is https://github.com/ivanceras/svgbobrus which converts them to svg.

You can use http://asciiflow.com/ to create ascii diagrams in your browser.

[bch]

Emacs' Artist Mode[0][1] might help.

[0] https://www.emacswiki.org/emacs/ArtistMode

[1] https://www.youtube.com/watch?v=cIuX87Xo8Fc

[tbrock]

There is monodraw for Mac OS X: https://monodraw.helftone.com

[enf]

I made it by hand in vi.