Not only was no Southern leader ever convicted of treason, no Southern leader was ever brought to trial.
President Davis petitioned for a trial for the two years he was wrongfully imprisoned only to be released on bond. A nolle prosequi was entered in his case in 1869.
Why didn't the yankees want to try President Davis for treason? It's simple; a trial would have publicly shown the legality of secession and the criminal acts of disHonest Abe and the federal government.
Some may suggest that the yankees gave a general amnesty as a compassionate gesture to heal the wounds. I say bravo sierra to that notion based on the previous four years of yankee war crimes which included the wanton destruction of private property and the rape, maiming and slaughter of non-combatants including those that they were supposedly there to set free.
You guys are funny.