The Bible does not say bigamy is ok.
It records instances of it. I puts in a couple of protections for extra wives. But it neither prescribes nor condones it. Just acknowledges it.
Actually, many stories in Scripture serve as cautionary tales about the serious problems that arise from it.
Even Adam had two wives. Lillian was his first wife and even was his second wife. They all lived in harmony. Probably explains how the world was able to happen since even only had three sons. Cain, Abel and Seth.