While they've (apparently) got the requisite two witnesses to the same act, my understanding of treason is that it more or less requires a state of war exists between the US and A and the nation to whom the accused gives 'aid and comfort'.Michael Flynn has requested a recess after the judge asked government attorneys whether he could have been charged with treason. The court is now on break until 12:30.
Something can be treasonous without being the criminal offense of treason imo.