He hasn't learned to put himself back to sleep. He is depending on you to do it for him. It's important for a child to learn to self-soothe. You will be doing him a big favor by helping him learn to do it.
Put a chair in the middle of the room. When he wakes, go in and put him back in the bed and then go sit in the chair. Don't talk, don't look at him. Don't let him get out of the bed. If he tries to climb on you, walk him back to the bed and then go back and sit in the chair. Do it 30 times if you have to. He'll get tired of it and he'll give up and lay in the bed. Let him cry if he wants to. You are still in the room.
After a few nights when he starts laying down and staying in the bed without getting out, and when he stops crying, move the chair closer to the door. Do that a little bit more every night until the chair is in the doorway. He will still know you are there.
After things go better, only put him in the bed and then walk out. If he comes back to you, walk him back to the bed, over and over. Hopefully it won't come to that. Hopefully he will stop waking. That's the goal.
You have to change the cycle. This is the way to do it. You have to be 100% consistent. Don't sit on the bed with him. Don't pat him on the back. Don't talk or engage with him. Don't move around. It is worth the work.