Rainbow Yggdrasil

In a white world tree, the rainbow world tree stands... -On that day, I woke up in a white world. I had no memory before I fell asleep. The only thing I remember is that I am "human" being. In my sight, there is a vast world of nothingness... and a huge world tree shining in rainbow. Why has the world become like this? What does that world tree exist for? Why I can recognize "that" is a world tree by just one look? I must understand about this world and about myself. I had nowhere to go anyway, so I started walking to the tree.