The top hole is the nest hole. It too a very long time for the pair of red headed woodpeckers to make it home. The hole below was a test hole I guess. There are several others in nearby dead branches.
@pusspup Good point. A bit of research says that the entrance hole is 2 inches in diameter (5.08 cm) and nest area is 8-16 inches deep (20.32-40.64 cm)