Okay for anyone who knows anything about chemistry, can you please explain this to me?

The molecule HCO3- is called "Bicarbonate"

But that doesn't make sense to me.. If Bi means 2, I don't see 2 of any element in that molecule. There is 3 Oxygen atoms, but that would result in a "tri" prefix not bi.

Can someone explain this to me please?

gracias.