UPDATE:Thanks for the FP,guys!

People die and are thrown deep underground.They fight and fall on the battlefield.This makes no difference however to the entity known as The Red Oak,a large tree like colossal creature bent on taking over the land by leeching of the vital energies of the soil,while its roots spread out and crush towns and kingdoms alike.It emanates a dark aura from it's roots that infects the fallen corpses of every creature be it man or beast.The curse sprawls wicked roots and branches underneath the skin of the body,starting from the victim's brain,taking control and bounding it to The Red Oak's will.These arisen walkers are known as Rooted spawns.They act pretty mindless and docile if left alone but if they happen to be at a close proximity to one of The Oak's roots,they start to act organized,become faster and more deadly and self aware of their surroundings like a hive mind.

Some corpses can merge into one bigger entity known as a Branching overseer as seen here: http://www.newgrounds.com/art/view/thepsychosheep/branching-overseer