Need help? My 3 yr old is biting in preschool. I don't know why he is doing this. He bit me once 2…

Need help? My 3 yr old is biting in preschool. I don't know why he is doing this. He bit me once 2 years ago and I put a stop to it quick. Usually when he is aggressive at home he is reacting to something like being placed in time out or not getting his way. I can't seem to get a answer if the child he bit did something to him first. Any words of wisdom? He has a 1 year old sister but is very loving majority of time