There is really no reason for the tree (s) unless God knew that he had angles (sic) that were already bad in their 'hearts'.
He did know this, dear Sayswho... peace to you!
The physical realm was created for the purpose of hiding the seed [of the Woman] from its enemies in the spirit realm. "Treasure... hidden in earthen vessels". The greatest of such enemies is Death... the "last enemy." And there are others; however, the Adversary (Belial, called "Satan" and "Devil") wasn't known to be among these. He joined such forces when he became jealous of the One whom he was supposed to protect... the Copper Serpent/Propitiatory/Tree of Life... Christ... and the ones whom that One protects (the seed of the Woman).
Adam and Eve had virtually all they could want, even eternal life (as they could eat from the Tree of Life without limit). Unfortunately, they both wanted something they were not PHYSICALLY ready to possess: knowing "bad"... meaning, knowing death. While the spirit can know death... and live... the physical body, at that time, could not. It has not been brought to its maturity, yet. Since it never realized that potential but basically ceased moving toward that end and reversed so as to go BACK to the earth... and since that is the body WE inherited, ours cannot with. Not yet.
Eve was tricked into believing that was not the case, however - that she would eat and be like God... not only knowing good (life)... but bad (death)... yet living. Adam, however, knew it was the case; he believed, however, that he could "conquer" death (as his brother, Christ, eventually did) and so sold the lives of his progeny for that prospective ability... which he did not receive. Because it wasn't anyone's to give, but God's. And He didn't give it to Adam. He did, however, give it to the Last Adam, Christ.
I hope this helps!
A slave of Christ,