Inconvergent's writeup on growth is absolutely worth a read if you like this stuff.
See the Pen Growth Explorer by George Hoqqanen (@hoqqanen) on CodePen.
See the Pen ProcGenJs -- Grow by George Hoqqanen (@hoqqanen) on CodePen.
Before going over this, it'll be useful to have seen the page on random walks first.
See the Pen Brownian Trees by George Hoqqanen (@hoqqanen) on CodePen.