Let me just add a disclaimer: I'm not implying Confederates are on the same level as Nazis, just that by having a similar process to Germany after WW2 wouldn't national healing have been accelerated?
Interestingly enough, this question was just asked yesterday. See below for the thread, and my response. Feel free to ask any follow-ups! TD;LR - Lincoln's decision NOT to hold tribunals was a direct, conscious effort to accelerate the process of national healing. To have held such trials was thought to be a rebuke of efforts to come back together to heal.
https://www.reddit.com/r/AskHistorians/comments/6tios5/why_were_there_no_nuremburgtype_trials_for/