Jerry is right: You can't say "a bunch of student" The question marks after the sentences confuse me. Are they part of the sentences? I have difficulty imagining anyone ever asking the question “There has been a bunch of students?” Anyway, this is my opinion: “Bunch” can have two different meanings that are relevant in this context. It can mean “a lot” and it can mean “a group of people” If it means “a lot” then it should be “There have been a bunch of students”. If it means “a group” then it should be “There has been a bunch of students”. For additional information, make sure to read Su.Ki.'s comment on my answer.

I think .. the correct sentence is There has been a bunch of students .. it's like (there is a bouquet of flowers)

Can we say a bunch of student? No, this is incorrect. A bunch is always plural.