Based on Gen 2:9

God created the Tree of Life and planted it in the garden. It was given to Adam and Eve to lengthen man’s time in the garden with God, to provide spiritual sustenance, to give him long life. It was the compliment to the food of the other trees, which gave their fruits for bodily nutrition and also the four rivers which provided the element of water to drink, for their thirst.

This trio of elements seem to mimic the Holy Trinity. God is One, yet present in three essences. God the Father is the giver of life, and the anchor of humanity where as He is deeply rooted, and He lives forever (Proverbs 1) and through His provision only can we live forever. The food is the body of the Son, Jesus, which is given to us freely and through His life we have spiritual nutrition to continue on, think about the Communion. And the Holy Spirit is the water, or spiritual flowing in our lives. Anywhere there is water in a dry land there is life and success. Think about rivers in the arid plains or an oasis in the desert. There is always growth and vegetation and life along those bodies of water. The Holy Spirit quenches thirsts and through His presence and our submission to Him in our lives we don’t just survive, we succeed.
Then there is the Tree of Knowledge of Good and Evil. The tree itself is not evil, but the desire of it is a temptation. And by eating of it, Adam and Eve were disobeying God’s direct command, a direct sin or disobedience of God. The knowledge of good and evil is symbolic of being like God, to be at His level of authority. It is Satan who overtakes the lowly serpent and then continues on to Eve, as he is now on an ambush attack of God’s newly created chain of command. He tempts Eve, and subsequently Adam, and promises that they will become like God. His temptation is dangling their so called “independence” in front of them. That they will themselves become like God. That they would be “free from His tyrannical rule”. That they would be able to “do whatever they want to”. That they would “no longer have to be accountable to Him”. And he also tempted them that they would not have to rely on God or His Tree of Life to live anymore, but that they “would surely not die”. And once they took that fruit and ate it, they saw that they were naked. Their eyes were opened to their smallness and mortality as humans. And as a response to their plight, they sewed leaves together to cover their sin. Leaves of God’s creation. Leaves which God made and man could nearly see through. What a trifle effort! They tried to cover their sin with the leaves of a tree. This was not only an admission of guilt but a demonstration of their inability to properly handle the situation. But God, He used the skin of an animal, and therefore its blood, to completely cover for their sin. He made for them clothes. A real covering. The blood which would eventually set man free, through the sacrifices of the Jews, and then finally with Jesus. The tree of Knowledge of Good and Evil was NOT able to free them, only condemn them. And once they were banished from the garden they were no longer able to eat from the Tree of Life either. They would surely die indeed. They would no longer have access to the fresh waters, the nutrient fruits or the life giving tree. Everything had changed, everything had fallen. 
God had a plan, and though it would take a couple of thousand years on earth to come to fruition, it had been started from the moment of Adam and Eve’s sin. Planned since the very idea of creating humans crossed His mind.
So now we come to Jesus, fully God and fully man, He was born into our sinful world and placed in a manger made of wood. To me I see that this symbolizes our own birth into the results Adam and Eve experienced from that Tree of Knowledge of Good and Evil in the garden. And how every attempt of our own to “balance our lives in more good than bad”, or that “I’m a good person”, or “I’m not as bad a person as so and so”, is like sewing fig leaves to cover our iniquities. It takes more than that to appease the penalty of sin, which is death. (Romans 3:23 and Romans 6:23)

And then Jesus died on the cross, symbolic of the defeat of the penalty of that tree in the garden, the Tree of Knowledge of Good and Evil. And by so doing, he brought us back to the only tree that matters, the Tree of Life. The Tree of Life, through Jesus, reconnects us into eternity with God once again.