Hey Ananya

To join Indian Army after graduation, BTech particularly, one does not need to have a specific branch or course in Engineering if applying through Combined Defense Services (CDS) after graduation, you should clear the minimum eligibility criteria and the entrance test+SSB. CDS

And if you're applying for recruitment through AFCAT, then for different Engineering posts you need to have specific course study in your Graduation. For example: For an Aeronautical Engineer the courses allowed are:

Aerospace, Aeronautical, Mechanical, Industrial, Automation, Mechatronics and other specializations. If you want to know more, follow the link; AFCAT

Other than AFCAT and CDS, Indian Army organizes recruitment camps where candidates are selected on the basis of simple test and physical test for lower posts in the Indian Army. For that you must see the official Join Indian Army website.

For further doubts, ask us. All the best