Four monks came to the Buddha and asked him for a topic of meditation. He gave them various topics and they, having retired to various places, all became arahants: one by understanding the six-fold sphere, the second the five khandhas, the third the four mahábhútas, and the fourth the eighteen dhátu. They returned and related to the Buddha each the particular excellence attained by him, and one of them asked the Buddha how all these methods could lead to Nibbána. The Buddha related a story of the past where four sons of Brahmadatta, king of Benares, having asked their charioteer to show them a kimsuka-tree, are shown the tree at four different times: when the buds were just sprouting, when the leaves were green, at the time of blossoming, and at the time of fruit-bearing.
When asked to describe the tree, the first likened it to a burnt stump, the second to a banyan tree, the third to a piece of meat, and the fourth to an acacia. The matter was referred to the king, who solved the difficulty.
The king was the Bodhisatta. J.ii.265f