The Tree of Life represents salvation through God’s grace and eternal life. It’s in heaven one but we see it again in Revelations 2:7.
The Tree of the Knowledge of Good and Evil represents the law for righteousness, which is the idea that one can achieve righteousness through a set of laws, observances, rules, etc. Or in any other way than simply relying completely on God. That tree was destroyed in the Great Flood and, in fact, was cast into hell (Ezekiel 31).
The two trees then symbolize the old and new covenants as well, and in the process condense the whole message of the bible down right there in that one story. Follow the law or follow God. The law will lead you to hell. God’s grace, to eternal life.