There are lots of people tried for treason... Aaron Burr, Benedict Arnold, the Rosenbergs, this other CIA spy recently (can't think of his name), and a bunch more. Jane Fonda was never tried for treason because she never committed treason in the legal sense. She spoke out against the war and was very active in pro-Vietnam relations which is not treason. It's not like she sold nuclear secrets or similar. She was just called a traitor by vets across the U.S.

Unless I'm wrong. Someone please correct me if I am. This is the extent of my knowledge regarding Jane Fonda and "treason".