What is this??

My dog is a Shih Tzu mix. He’s had this thing on him for years but lately it’s been growing bigger. The vet says it’s nothing to be concerned about and would only be removed for “cosmetic reasons”. He’s been licking it more than ever and it bleeds when I comb over it. The pics are when we first noticed it up until today. Should I get a second opinion? If I posted to the wrong thread please guide me.