What exactly does the Etz Chaim mean?

I’m a bit confused about what the Tree of Life is supposed to mean and what it represents. Peter Mohrbacher uses it as a kind of “road map” of heaven in his book Angelarium, but that’s a work of fiction. From what I understand it’s something of a metaphor for the human person? Or of god? Or the process of learning?

I am entirely lost on it to be honest.