I won't cover the same ground as the others, so here is my take. Adam was never meant to 'know' evil. God NEVER created evil-God is ALL Goodness, to say that God created evil is the antithesis of God. When we see in Isaiah 45:7,"I make peace, and create evil", the evil he is talking about is translated calamity, something the Lord does when evil doers go about their way without concern for God.
Evil was present in the Garden in the form of the serpent-who was Satan, the Opposer. God created a good angel, Lucifer, or light bearer, until he rebelled against God. God 'allowed' Satan to have access to the Tree of the Knowledge of Good AND EVIL. Since God only creates good, this is Satan's Tree. These Trees are Figurative, since a mere 'tree' cannot give one knowledge. The other Tree, the one Adam and Eve should have eaten from was the Tree of Life, of which there was no commandment. Eat all you want and can from the Tree of Life. This Tree is Christ, who's flesh is real food, and who's blood is real drink.(John 6:55)
The choice is simple, by God placing or allowing to be placed in the Garden, the Tree of the Knowledge of Good and Evil, God gave man a choice-serve Me, or serve My Archenemy, Satan. Man was to eat from the Tree of Life, recognize(not 'know') evil and flee from it. Instead, he betrayed his True friend and Creator, sided with His Archrival, and became as deserving of death as Satan.
Both Trees were restrained from man; man cannot eat from the Tree of Life(Christ) and be joined to sin, and God prevented Satan from exposing the Tree of the Knowledge of Good and Evil before man could witness His Son and know salvation. But both Trees are now revealed for all to see; Christ, the Lamb of God for all men to eat His flesh and drink His blood and live forever, and the Tree of the Knowledge of Good and Evil, the means by which men can become 'gods'-like Satan, fulfilling their lust for power by accessing 'knowledge' apart from the Tree of Life. This Tree is called 'Anti-christ'.