It's not a tree since you have transpositions. It's a directed graph, since it has cycles.
It does not have infinite cycles because of the 50 move rules and repeated position rules, so the same position is not necessarily the same state/position. Or depending on how you model the data structure, cycles at all.
alt Hacker News
It does not have infinite cycles because of the 50 move rules and repeated position rules, so the same position is not necessarily the same state/position. Or depending on how you model the data structure, cycles at all.