You have a sapling that produces weird fruit each and every week. Each one of these fruits is a devil fruit, each one possessing mystical and strange powers that seem to be born of the dreams of humans. As time passes and the sapling grows, the time between each fruit decreases and the number of fruits it produces increases. Any devil fruits that have already grown on the tree will not regrow.
When a devil fruit user dies, their fruit is reincarnated as the closest fruit of the same type as the original devil fruit. If no such fruit exists, it will have a chance to regrow on the devil fruit tree, but it is not guaranteed to regrow the next time the devil fruit tree blooms, so a devil fruit might never reappear if its base fruit becomes extinct.