If he is biting, you need to stop feeding him treats from your hand; give them from a bucket for now.
When he does bite, immediately make him back out of your space, and make him STAY out of your space until you invite him back in. If you can catch him before he bites; meaning you need to develop 'eyes in the back of your head', take his muzzle in your hands and vigorously rub his muzzle until he gets tired of it and moves back on his own; this works, and does not make the horse afraid of your touch.
I agree with the above poster, too that he may just have an active mind, so you may need to just DO more with this guy; more ground exercises to keep his brain working and occupied, more ring work to keep him learning too, etc.
"The ideal horseman has the courage of a lion, the patience of a saint, and the hands of a woman..."