Feeding the "Tree of Wisdom"
There comes a time in the game where you have nothing left to spend your money on...except the Tree of Wisdom. It's essentially a late-game money sink so you have some vague reason to keep playing and keeping track of how much you've amassed.
I would recommend holding off spending your money there until you don't have anything else you want to buy.
I have bought everything, so I have a TON of wisdom tree food. It is at 300 feet so far, and I want to get to 1,000 because it lets you do cool tricks in-game.