When you level up in Tallest Tree, we make sure a new tree is planted in the real world. We do so by donating money to various non-profit organisations dedicated to protecting the environment. Currently, donations are made to Trees For The Future. We do the donations in bulks of 1000 trees, meaning your trees will be planted along that of other players. Because the game is still early in development, it may take a while before the donation is made, since we need to reach at least 1000 trees first.
If you have any questions, reach out to us at firstname.lastname@example.org or head over to our Discord server.