Hmm. Considering I understand correctly what you mean by saying “save choices”, then in the example Dialogue Tree (downloadable examples file). I am saving choices by setting (and checking) a boolean blackboard variable for each choice that needs to be saved.
Blackboard Variables on their turn can also be saved/loaded (to json or player prefs) so the choices (in this case) would become persistent between game sessions. Please let me know if that works for you, or if I misunderstood your question. 🙂