Developmental delay. Seen so far is!

Hi, my son is 2 years old now and he has not started speaking yet. We try to talk to him but he gets a bit aggressive. Sometimes he had spoken words like ma and nana but not too frequent. He is going to school got the past 2-3 months and he has not had many difficulties adjusting there, he eats and has fun there. He plays with the teachers and helpers as well. He loves going outside and play with swing and slide. He does not cause any issues in eating food and also tries different foods as well. The only issue I have seen so far is regarding speech delay. Can someone please let me know if there something I need to do to make him speak and communicate. Although he is very young but as per general developmental milestones he seems to be behind in this aspect. Would appreciate any advice, thanks.