It's possible to grow a money tree in Animal Crossing: Wild World! To grow one, you need a Golden Shovel and a bag of money. Your town can only have one money tree at a time, so don't try to plant more than one at the same time.
When you bury a bag of money, it will sprout like a normal tree. That sprout will grow into a fully-grown tree in four days, and it MIGHT be a money tree. However, small bags of money are unlikely to grow into money trees. Large bags of money have a better chance of becoming money trees, but you will never have a 100% chance of growing a money tree no matter how much money you bury. To have a 1% chance of a tree growing into a money tree, plant 1,000 bells. To have a 14% chance, plant 14,000 bells. And so on.
To get a large bag of money, you can go to your pockets, and drag the stylus from the wallet to one of the open pocket spots. You will be able to choose how much money to put in that money bag. Also, your wallet can only hold at most 99,999 bells, so if you get paid more than that, or withdraw more than that from the bank, the rest of the money will appear as money bags in your pocket.
A money tree will always grow the same amount of money: 90,000 in three bags of 30,000. The amount of money that you bury does not affect the amount that the money tree grows on it. It is always the same. You shouldn't bury 90,000 bells or more, because if a money tree does grow, then you won't be making a profit. You should bury a smaller number than 90,000 so you can try to make a profit.