Help:(

So I need some good advice please. I have a 11 month old and a newly 2 year old in July. So my oldest is MEAN to my 11 month old it’s awful. He hits her pushes her and always out to get her and I don’t get why. There’s not even a reason he just does it!!!! He will just come up and push her down as she is walking and learning to walk. I try to get onto him but it never works. Never. He still hurts her all the time. And when he’s not with her and I have just him he’s a great kid. It’s like when she comes around he’s evil!!!! Anyone else go through this? How did you fix this issue?