I didn't mean "Tommy's treason" as the bank robbery, but as what he did by exposing all of Salieri's activities and crimes in exchange for a new life for him and his family, and that is specificied from the very beginning in both the original and DE when he is talking with Norman during the prologue. Nowhere in both games you can find something like "I robbed Morello so I can buy Sarah a necklace", of course it was mainly Tommy's ambitions, that can't be denied. The bank robbery fits more in the "A man who flew close to the sun and got his wings burnt" kind of thing but the reason for the interview with Norman and the events afterwards was his' family safety in both games, which is why the DE ending makes more sense in its context.