Why is there this lump of gum on my tooth?

I have this gum lump on my 2nd molar (tooth 18) and it has what looks and feels like a corn kernel on it. I try picking it out and it starts bleeding. I do not have my wisdom teeth yet. My mother offered to take me to the dentist but why should I if I don't' know what it is. The lump is connected to the rest of my gum and is right on top of my tooth. My mother also said that it is just a tooth that is growing in but my dentist said that all my teeth have grown in except for lateral incisor (tooth 7) which is more than likely hereditary after getting an X-ray. So what is this lump and should I go to the dentist because of it?