I really need to tame my dwarf hamster because he bites a lot, any tips?

He will take treats straight from my fingers & lets me pet him at times. But if I try to put my hand in the cage and let him take a treat off my hand, he bites really hard. It hurts so I'm kind of scared. I want to be able to pick him up but it's not working out. What should I do? Maybe try training him outside of his cage?