After 12th you can do your graduation with any of the field there is no any restrictions for banking preparation only you should have good preparation for the exam to get success.

U can do any graduation degree as u want... Bt bank k liye prepare hotein rahein

Great. You can do BBA/Bcom which will help you to form your base in banking. There is a specialized course in banking at graduation level like BBA in banking and Insurance.

So you can choose this field.
Also you had maths so this shall help you overall with banking studies and course.
Later go for masters as per your interest and need.

Good luck.