Apple makes a strong point about Tom's brushoff of Fredo at Mama's wake. Yes, he was doing Michael's bidding at that point. But I also believe there may have been a personal reason for Tom's coldness to Fredo then. Mama's death occurred after Michael's initial Senate testimony--and the fateful boathouse meeting in which Fredo told Michael that Pentangeli was alive and that the Senate lawyer, Questadt, "belonged" to Roth. Tom should have known both--and he didn't. Fredo's perfidy made Tom look bad in Michael's eyes. It probably also convinced Tom that Fredo may have been more malicious than he thought.