There were conflicting reports and, as others have said, we just don't know what the Bulls were asking for but let's not forget that Chicago never actually wanted to trade Butler. From what I've gathered is they wanted multiple Brooklyn picks and multiple rotation guys. So it was probably something like #3, Brooklyn '17, Crowder, and Bradley. Maybe there was another pick asked for as well.
At the end of the day, whatever it was, Ainge thought it would be too much for Butler and he was probably right.