Why tricuspid valve has three cups and why not bicuspid valve?

Dear student,
Please find below the answer:

The tricuspid valve has three flap-like cusps. It is present in between the right atrium and right ventricle. It helps to prevent the blood from regressing back into the right atrium. The tricuspid valve regulates the blood flow in the right side of the heart.    

Hope this clears your doubt.
Regards.