To get the tree warps (the giant trees that are an area in themselves) you must first help their father Tibor.

After defeating the thieves in Verla, head back to the crossroads and walk to the biggest tree. He'll ask you to help him out. Inside you'll encounter a lot of corpses and the ghosts they spit out. At the top is a giant knight, whom is considered a boss.

After he's defeated, Tibor will repay you by asking his children (whom are all twins) to take you to their twins. You must visit both trees before they will warp you to their twins.