The Confederate flag is not treason. Confederates were not traitors. Only those who owe allegiance to the US can commit treason. Once the Southern states seceded, their people no longer owes allegiance to the USA. The Confederacy was not form until AFTER the first states seceded. Those who were later admitted to the Confederacy also seceded first.
They were enemies of the USA, not traitors to it.
They weren’t trying to DIVIDE the nation. They were trying to LEAVE it and create their own.