wait, i thought trees are directed (parent → child) acyclic graphs, not undirected?

“In graph theory, a tree is an undirected graph in which any two vertices are connected by exactly one path, or equivalently a connected acyclic undirected graph.”

https://en.wikipedia.org/wiki/Tree_(graph_theory)

Technically it’s undirected. The nodes are often defined as parent to child but you can have a child pointer back to parent too.

great! I finally found this article