Controller Tree

Basic idea was from the plant mutants, but going with a stationary design rather than mobile.

The premise is that the tree grows fruit year-round, but those that eat of the fruit are now vulnerable to the tree's control.  The tree will attempt to gain control over other creatures, and the older the tree, the more complex its thinking can be.

For example a basic tree might just convince creatures to gather near its base to fight each other so that their bodies will provide better fertilizer.

A more advanced tree will have enough intelligence to encourage the locals to form a town around it, so their dead bodies get buried near the tree (for fertilizer).  It uses its fruit more subtly, so the town works together much more effectively.  There is far less wealth being hoarded, far less poverty, but the local tree is working on breeding better people in the town so it has better servants.  Residents of the town are far less socially skilled as most of the social problems are covered up by the fruit forcing loyalty.

Wastelanders might get lured in by the various loot around the base of a small tree, but if they eat the fruit from the tree they might try to kill their companions.  There might also be a large predator at the base of the tree gnawing on one of the fruits, and it will attack people, eating their bodies, and defecating near the base of the tree (to fertilize it).

A larger tree would be a large central tree in a town, and the meals served to the people contain small samples of the fruit so the residents simply get along better.  The larger tree would try to manipulate the town to have an optimal health among the people, proper cleaning/filtration of wastes, etc, all to make sure that the tree has plenty of food.  It will have farms around its perimeter in order to keep its people healthy, even though some of the fertilizer is diverted to those farms.

Possible upgrades might be the tree growing sub-trees via runners, a clonal setup communicating via underground root system like the Pando, or just larger fruits that contain smaller intelligences that are a copy of the main tree.  These subordinate trees will tend to be 'allies' of the main tree, but the two still want their own sources of food.  Think Crown Shyness, but on a political level rather than physical contact level.

A PC from one of these tree-controlled towns will have slightly better mutations and physical statistics, but much poorer social skills to recognize deceit in others and lower will to resist others asking for help.  Level of improvement depends on the age of the tree, aka GM's choice.