I’m not an attorney but his other crimes do not go to the level of treason. He may have known about the voter fraud but did not partake in any of the activities related to the fraud until he takes the oath of office KNOWINGLY it was stolen for his and the party’s benefit.
What about the money that he took from foreign governments when he was VP? Is that not treasonous - working against your own government, using your position in government for your own financial gain?
I equate that with selling out your own country. Granted, I do not know the law and how much is needed to reach the Treason Level.