[207] Bhikkhus, suppose there were a great tree, and all its roots — both those going downward and those going crosswise — draw the sap upward. In this way, bhikkhus, with that as its nutriment, with that as its fuel, that great tree would stand for a long time, for a long stretch of time. So too, bhikkhus, for one who dwells contemplating gratification (assāda) in things that can be clung to (upādāniyā dhammā), craving (taṇhā) increases. With craving as condition, clinging (upādāna); with clinging as condition, existence (bhava) … Thus is the origin of this whole mass of suffering (dukkha).
English translation from the Pali (Siam Raṭṭha edition) — under review, not for citation.