The Withered Tree was a secret cult active in Gondor, especially Minas Tirith, in the late Third Age.The Cults religious indoctrination and loyalty to the dark lord was restricted to it's leadership and most fanatical core, to the outside they appeared mainly as a political group.They sought to sow seeds of despair and distrust in gondorian society and their agitators doubted the Stewards authority to rule, mourned the absence of a true King and the decline of formerly powerful and proud númenórean culture and spirituality, often accused , more commonly in subtlety rather than open challenge, the Lords of Gondor of selfishness and unreasonable acting, of following outdated ideals and traditions, ready to sacrifice the lifes of common people in a suicidal war that could not be won.
Although the groups rants were confused and contradicting, most of it's members actually were not evil, but misled and desperate, an odd mix of idealists, cultural pessimists, self-castigators overcome by fear and doom and sometimes simple cowards.