According to Indian Citizenship laws, a person is an Indian

1. By birth if born in India on or after January 26, 1950, but before July 1, 1987. 
2. If a person is born after July 1987, he or she can claim citizenship if either of the parent is a citizen of India. 

3. For those born in India on or after December 3, 2004, they can claim  citizenship by birth only if both parents are Indians, or if at least one of the parents is a Indian citizen and the other is not an illegal immigrant at the time of birth in India. So along with one's birth certificate, both parents citizenship proofs would be required.

If you are all Indians by birth, you should choose Indian as your Nationality.