A little boy used to play in the shade of a tree. One day the boy sat leaning against its trunk; he cried and sighed. I am hungry.
Eat my fruit said the kind tree. And it bent down one of its branches. The little boy had his fill of the fruit and felt satisfied.
Long years passed and the boy grew up. Then once again he sat under the tree with a look of dejection and hopelessness. What is it? The tree asked. My wedding day is barely a week away and I have nowhere to live. Cut down my branches and build yourself a house, said the tree. The young man set in work immediately.
Time passed and now the young man was a sailor. And once again he sat under the tree with a look of remorse on his face. It again asked what the matter was. He pleaded, “My captain is cruel, so to survive, I must own a ship.”
Cut down my trunk and build a ship.
The sailor  grew old but once again he turned to the tree with a laden expression on his face. It was cold and the  sailor leaned on his stick trembling. “Make a fire of me”, said the stump of the tree. It so on burnt in the fire softly humming a tune.
Define the friendship that this story illustrates.