Adam and Eve were placed in a garden. Trees in the garden represented mankind that were neighbors.
Tree of Life was God and tree of knowledge of good and evil was the Devil, also known as Serpent. The Serpent is the same one that is mentioned in the book of Revelation. Because angels are not human, the one that was evil had to be possessed by the devil, same as today.
Eve was seduced by the devil and she did eat, meaning she had sex.
Gen 3:13 And the LORD God said unto the woman, What is this that thou hast done? And the woman said, The serpent beguiled (seduced) me, and I did eat.
Gen 3:14 And the LORD God said unto the serpent, Because thou hast done this, thou art cursed above all cattle, and above every beast of the field; upon thy belly shalt thou go, and dust shalt thou eat all the days of thy life:
Gen 3:15 And I will put enmity between thee and the woman, and between thy seed and her seed; it shall bruise thy head, and thou shalt bruise his heel.
Thy seed (evil children) and her seed (good children).
This is still going on today, children of the Devil and the Children of God are real people and both are still in a battle. The only thing is, the devil knows who the children of God are, but Christians don't know who the children of the Devil are. Read the words of Jesus in the Gospel, because he knew.
Cain was of the Devil and he murdered Abel.
1Jn 3:12 Not as Cain, who was of that wicked one, and slew his brother. And wherefore slew he him? Because his own works were evil, and his brother's righteous.