Typical leftie you ignore the facts that void your ideas. Here is the legal definition of treason.
"18 U.S. Code § 2381.Treason
U.S. Code
Whoever, owing allegiance to the United States, levies war against them or adheres to their enemies, giving them aid and comfort within the United States or elsewhere, is guilty of treason and shall suffer death, or shall be imprisoned not less than five years and fined under this title but not less than $10,000; and shall be incapable of holding any office under the United States."
The South had announced it's intention to secede from the Union thus renouncing citizenship meaning they no longer have allegiance to the Union. So sport they did not commit treason.