Inspired by a post on reddit asking about a PC wanting to build an airship, I had this idea. It would be a very, very rare type of tree, making it an ongoing quest to find enough to make planks for a ship.
Feel free to use this for your games, but don't forget to account of the demand for such a tree, growing time and possible difficulty in growing more, disgruntled druids and fey, penalties for poaching such rare trees, and thieves on the lookout for wood from said trees.