"This whole concept of treason against a particular state is very puzzling."I haven't a clue how to try to explain it because it seems perfectly natural to me and I find your puzzlement totally baffling. Prior to Lincoln, the States were sovereign, so why is the concept of treason against them puzzling?
Maybe my puzzlement comes from the fact that he wasn't a resident of Virgnia. How can someone commit treason against a state they never lived in? That would be like Nazi Germany charging American POWs with treason against ther Riech and executing them for it. Maybe they should have charged him with invading Virginia?