To retrace my steps: I searched on google for [ascii tree generator] and, alongside many results about generating output for directory trees / folder structures (like that of tree: http://mama.indstate.edu/users/ice/tree/), I found this "Show HN" submission: https://news.ycombinator.com/item?id=21042390 . I installed and tried the linked project (https://github.com/spandanb/ascii_tree) and it kind of works, though I had several issues (posted later at https://github.com/spandanb/ascii_tree/issues/3). So I gave up and just copied the tree from that thread's top comment, by user kps (https://news.ycombinator.com/item?id=21043091) and manually edited the tree in Emacs to add new nodes by copying things around.

Additionally, after posting the comment to HN from desktop, I happened to notice within the 2-hour edit window that it looked awful on mobile (as does the comment I copied from: probably a bug with the default font stack used by Chrome on Android not using monospace versions of the box-drawing characters), so I edited to replace "─" with an ASCII "-". It looks less perfect on desktop, but less poorly aligned on mobile, so is a reasonable compromise.