Many cultures have a Tree of Life concept. In Nordic mythology, the Yggdrasill is the World Tree which connects the nine worlds.
The tree itself is believed to be an ash tree. Ash symbolizes combining strength and wisdom during times of sacrifice (see Nature-Speak by Ted Andrews). In fact, the Norse god Odin hanged himself from Yggdrasill so that he might achieve higher wisdom.
Below the Yggdrasill are three roots and three wells. Running along the branches of the tree are four deer, representing the four winds. At the time of Ragnarok (the end of the cosmos according to Nordic myths), the fire giant Surt will set fire to Yggdrasill.
I love how one story encompasses the four elements (earth, wind, fire, water), explains the connectedness of all things, and teaches about wisdom. Now that’s an epic story.