Mushrooms will grow on a tree if it is dying. Mushrooms are a fungus that can break down wood, so when a tree falls down or if it is hollow, mushrooms may appear on the tree.
Mushrooms are not a plant; they are classified in the fungi kingdom. It is a fruiting body that lacks green chlorophyll, which plants use to make food and energy.
Most of the growth of the mushroom happens under the ground or other growing surface, which makes it appear to grow over night. It can take days or weeks for a mushroom to fully develop.
While some mushrooms are edible, others are poisonous. It is best to not eat any wild mushrooms unless you are familiar with which ones are safe to eat.