Not much is known about the early history of Gregor, we do know he comes from Russia and immigrated to America to live with his sister who could help with his " problem". He found Mutant Town, to be what Russia could not be for him - a home. While he mostly hid his power from others including mutants, one day while investigating Mutant Town's underground Gregor forgot his medicine, the one which his sister always reminded him to take and he started to mutate. First, he started planting roots everywhere but was still mobile however when he fell asleep it overcame him and he became an entire living tree. How this affected his regular life is unknown but it's possible that Gregor can return to his human state with much needed help. While in his plant form, he requires all the needs of a plant including sunlight, fresh soil and space to grown.
After M-Day, he retained his powers with a handful of other mutants making him a possible candidate for the X-Men or any other band of mutants. Even further, his second power is that which today is very needed, the ability to cause mutations.
Gregor had the unfortunate power of growing into an arboreal form while he slept, making his chance to become a crime-fighter very short. While in his plant form, he is unable to move and needs a greenhouse with lots of space to grow and, as a secondary mutation, he can grow fruit that can kick start mutation or even enhance it.