The Buddha attained enlightenment sitting under a tree. He meditated on the chain of causation.
From ignorance spring body, speech and mind.
From body, speech and mind springs consciousness.
From consciousness spring the names and forms of objects.
From the names and forms of objects spring the six senses of seeing, hearing, smelling, tasting, touching and thinking.
From the six senses springs contact with objects.
From contact springs sensation.
From sensation springs desire.
From desire springs attachment.
From attachment springs birth.
From birth spring old age, death, grief, pain and despair.
In this manner the whole mass of suffering in the world originates.
Taken from 366 Readings from Buddhism.