Once upon a time a long, L-O-N-G time ago, the Earth was different. There were no people living then. The animals that lived then were very different. There were many swamps. There were many ferns and tall trees around the swamps.
One tree was named Cleo. Cleo soaked up the light from the sun. Like all plants, she used sunlight to make her food. Some of it she used to live and grow. Some of it she kept for later. She stored some energy in her body.
Millions of years passed. Cleo grew and grew. She grew taller. She grew more and more branches with more and more leaves. She stored even more of the sun's energy.