Hi Wendy,
This is a little late for your question, but still, someone may benefit.
Generally, the HCPCS code G0416 is only billed for prostate biopsies to Medicare. It's possible that you may have a specific payor that wants the G code instead of the CPT. But in most cases, you would bill a commercial payor (the Blues, Aetna, Cigna, etc.) with the CPT 88305 x the number of specimen biopsies you have.
When billing Medicare (or as directed by another payor) with the G0416 code, you only bill for one unit. It's all-inclusive, regardless of whether the pathologist did 6 separate biopsy specimens or 20.