The plea and co-operation agreement indicates that Paul Erickson knew she was a Russian agent and helped her carry out her assignments.
People will be throwing around the T word, but there are no treason indictments in peacetime. The Constitution defines treason very specifically, and even the Rosenbergs were not charged with it. Erickson could, in the worst case, end up being charged with espionage, which can carry the death penalty.