The Radiant Grove (Savage Worlds)

From publisher blurb:

In the lead up to the Great War, a cave system in a once-unspoiled park in western Wisconsin was turned into a dumping ground for radioactive and biological waste. Somehow in that toxic ground, a miraculous tree bloomed. In the darkness it ate the radiation rather than depending on light from the sun.

Fifteen years ago, a band of simians discovered this "Tree of Life" and built their home in it's branch. Their leader, Longmane, has long believed that a time will come when humans die off and apes inherit the Earth. Now the signs Longmane reads tell him that time is now.

The Radiant Grove is set in the Broken Earth setting, but with a little work can be used with any post-apocalyptic campaign.