I have been trying to grow a 2x2 dark oak tree. I have cleared out a 14x14 area and have put more than a stack of bone meal into it. There is nothing around it to prevent it from growing like grass, pumpkins, or melons. It has grown fine previously and 2x2 Jungle and 2x2 Spruce trees have no issue in the same place I am trying to grow the dark oak.