Is there any compitative exams after bsc in botany subject.

There are many scopes after B.Sc Botany.
You can go for the integrated MSc+PhD program. Tata Institute of Fundamental Research, Mumbai every year conducts the exam for entry into this program. IISc Bangalore also offers integrated MSC+PHD.
A few people choose MBA, a few pursue MS in some other subjects.
Through competitive exam you can qualify for respected jobs such as Bank P.O., special officers in Bank, SSC, the prestigious Indian Civil Services, state civil services, CAPF (UPSC), CDS (UPSC) etc.