This story is from Upanishad and is retold by Swami Vivekananda.
Once there was a huge tree with many branches. On its lower branch was sitting a bird. When it looked up it saw another bird on tree’s highest branch. The bird sitting on the lower branch ate some sweet and sour fruits and then jumped to the higher branch. It looked up and saw that another bird sitting on the highest branch. It again ate some sweet and sour fruits and moved to higher branch. It kept moving till it reached on the lower branch to the highest branch. When it looked up there was still that another bird. As soon as it reached the highest branch it found there was no bird except itself.
In this story the bird sitting on lower branch is jeevatman (human being) and the bird sitting on highest branch is parmatman (God) and the sweet and sour fruits are the birth and death cycles.
Dear readers in your opinion ‘What is God?’