Abraham did take Hagar as his second wife. However, it brought noting but chaos into his family. Hagar and Sarah end up despising each other and the child of each (Ishmael & Isaac) fought with each other to the point that Abraham had to send away Hagar and Ishmael into the desert where they ran out of water and survived only by the intercession of an angel.
Does this sound like a good example to follow?
While polygamy does exist in the Bible it is never portrayed as producing anything good.