A Ball Of Fire
Wild was big as Earth had gotten bigger after the apocalypse. So hundreds or even thousands of kilometres of green forest with no human life was a common occurrence on earth. Humans who were the rulers of the earth were now just a small part of it. But Humans were tenacious. So even though they were not the rulers any more, they still lived around the world.
But not like they used to. Without fear and wantonly. Now, Humans lived much more humbly. And their favourite place to live was walled cities. But not everyone was fortunate enough to be able to live there.
Some were stranded in their old cities with broken buildings and destroyed walls. Most of those people died.
But some lived by adapting and one of the best adaptations that humans made was probably their ability to become metahumans.
And in second was using the incredibly large trees as shelters. Not just a shelter but a whole civilization.