Just FYI...Davis, Lee, and other high-level Confederate officials were not tried because the U.S. government was very much afraid that its courts would rule secession completely legal and constitutional. To this day, the courts have NEVER ruled on the legality of secession.
That's certainly the argument made by some. However, when seeking to have his treason indictment dismissed, Jefferson Davis’s lawyers didn’t raise the constitutionality of secession as a defense. They raised clause 3 of the Fourteenth Amendment - stating that Davis' constitutional disqualification from public office was punishment and that trying him again for treason would constitute double jeopardy.
Davis' case was certified to the Supreme Court. As Salmon P. Chase and other justices considered the clause 3 argument, President Andrew Johnson granted a full pardon to all Confederates for the “offence of treason.” The point was then moot.
Justice Salmon P. Chase later ruled against the constitutionality of secession in Texas v. White, 74 U.S. 700 (1868). “The Constitution, in all its provisions, looks to an indestructible Union, composed of indestructible States.” Texas v. White at 725.