Theory:

The story is set in Dehradun, where the author lived with his grandparents. His grandfather planted a lot of trees in his house - lime, guava, orange etc., His grandmother was interested in flower gardens, that attracted a lot of butterflies. His grandfather planted trees also in the jungle beyond the riverbed. His grandfather had explained that birds, animals and humans need more trees in this world - we should replace every tree that we cut for our personal use; otherwise, the world will become a desert. They planted small trees in an island that is dry during summers and flooded during winters. Second World War started, and the author was sent away to a boarding school. He returned after several years to find that the small island looked like a lush green paradise - because of the trees they had planted had multiplied. He realized that his grandfather's dream of trees walking again had come true.