I am studying in a non-Muslim country; my other group mates are all non-Muslims. They want to give gifts to the professor before the exams, because this is a custom here. They think that if they do not pay they will not pass the exams. But I heard that this is like bribery. I told them not to give the gifts but they still do not agree. If I do not take part they will put my share also. When I go for the exam, I will get the benefit of it too. (That means I will also pass). What should I do? My all colleagues will hate me because they will pay my part and they are saying I am being unfair. Please tell me what I should do?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

A bribe is the money (or favor) given to make the wrong right and the right wrong. Some people give bribes to reach a rank which they do not deserve such as a degree, a profession, … etc.
What is given to get one's own right or to avoid being harmed wrongly, is not considered a bribe for the person who pays it, but it is Haram for the one who takes it.
So, if the student among you will not pass unless they pay some bribe, then it is lawful for them to do so, but it is prohibited for the teacher to take it. But if what you give is only a gift that does not influence the grades, then there is no harm in giving it, or his taking it. But it is safer to avoid any kind of gifts in this case.
Allah knows best.