Hello. I am Wulfin. This may be hard to believe, but you gotta trust me on this. I started up a fresh vanilla Minecraft world. After mining some trees and harvesting some Reeds, I climbed up the mountain, only to find Herobrine standing on a tree. He would disappear and reappear again sometimes on a different tree. I have provided some photos below. (It may be difficult to see him, I tried to keep a safe distance in case my game crashed.)