Mark 10:11 ESV And he said to them, “And he saith unto them, Whosoever shall put away his wife, and marry another, committeth adultery against her.”
This verse is against divorce, not polygamy. Ironically we have lots of divorce and very little polygamy in our culture.
It says nothing against a man who marries a woman and keeps her, and then married another woman.
In fact I think one could argue from this verse that if a man did NOT keep the first wife, he would now no longer be eligible to take another wife.