Minecraft wiki entry for Superflat_survival, associated text: It is recommended that you do not trade for dark oak saplings at this time, as the dark oak tree requires 4 saplings to grow, which requires you to gather 20 emeralds rather than 5. Also, this tree yields less wood compared to the large jungle tree and the mega spruce tree. If a trader offers a dark oak sapling for trade, simply ignore them for now and wait for another trader spawn.