The Tree of Life is an important symbol in nearly every culture. With its branches reaching into the sky, and roots deep in the earth, it dwells in three worlds- a link between heaven, the earth, and the underworld, uniting above and below. It is both a feminine symbol, bearing sustenance, and a masculine, visibly phallic symbol- another union.
You can read more about trees in the Bible HERE
My favorite Biblical verses about evergreen trees are these from (surprise!) Isaiah.