I want to do aerospace engineering,I have decided to do btech in other branch and then do my masters in aerospace. which branch i can choose

You must do btech in it only not possible by another branch if choose any other you have to work hard for gate exam

Since you have decided to pursue aerospace engineering, I think you should do B.Tech in that only. I am not sure which risks are you taking about in B.Tech in aerospace. Of course, it is your decision to make. If you have decided to go for some other branch, you should opt for Mechanical engineering