A couple things.
1) How long are your training sessions? Do you train until he gets bored or full and quits responding? If so, stop sooner. As they say in show business "always leave them wanting more."
2) What other rewarding elements come into play when you train? (e.g. do you get excited and cheer when he does extra well? Does he have toys he particularly loves that you could offer? See if you can start offering other positive things in addition to the treats).
3) Does he ever initiate training sessions or do you always do it? (e.g. my birds will frequently start offering trained behaviors to signal "hey, can we do that training stuff?") If you see him waving or saying a particular phrase or whatever he's trained to do, have a short little training session. He needs to know that he can come to you for fun things.
4) Start having surprise treats. Stash some in a pocket or keep a jar near where he hangs out. Occasionally walk up and ask for a behavior WITHOUT a treat in hand. If he does the thing, tell him how great he is and produce the hidden treat or run over to the jar to get him one. If he ignores you, that's fine too, just walk away and try again later. You want him to learn that just because he doesn't see a treat ready to go... that doesn't mean there's no treat at all. It's worth his while to respond, because you just might make one appear.
5) If you're not using intermittent reinforcement, start doing so. Vending machines are nice, but they're predictable and boring. Slot machines are addictive. Early in training, you want to be a vending machine while the bird learns what's going on. Later, though, you want to change over to a slot machine. The chance of MAYBE a treat, and maybe a regular treat or maybe an extra special treat... that keeps them on their toes.
Ultimately, you need to make sure that training is just the most fun, awesome game in the world for your bird, which makes YOU the most fun, awesome person. Eventually they'll decide you're fun even without the treats. Until then... just keep treating!
