Mine was taken from the anime "Oh My Goddess!" in which they talk about the aforementioned Norse Mythology, Tree of Life. Although in the anime, Yggdrasil is the computer system that controls things. I'm not in relation with "yggdrasil", just expressing where I got the name from. ^_^ Like yggdrasil, mine too now means Tree of Life. Although, it came from the anime when I first really thought about a screenname.