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Well, I was thinking that Satan had put the tree there because of James 1:13 which says- "Let no man say when he is temped, I am temted of God: for God cannot be tempted with evil, neither tempteth he any man"- but then looking more closely it does say- in verse 14- but every man is temted, when he is drawn away of his own lust and enticed and 15- then when lust hath concieved, it bringeth forth sin: and sin when it is finished bringeth forth death- so the original sin must have been lust for the knowledge that the snake knew of but Eve did not know about- Eve probably felt that God was hiding something from her and the lust to know if God really meant not to touch the tree or if he was just waiting for them to touch it so that they could know Him better by understanding what it was like being Him more than they did concieved in her heart which translated itself outwardly into her sinning by taking the fruit because the lust corrupted her trust- and faith at the moment and she quit trusting God for a moment and put her trust in Satan only at that moment- put at that moment she turned her back on God and put her trust in an idol- Satan's ideology of the tree- incomplete information.
Also Genesis 22:1- says - "God did tempt Abraham" which could also be translated- tested- so maybe the tree was put into Eden to test Adam and Eve just as God tested Abraham by asking him to sacrifice Issac- and then it turned out God did not allow Abraham to sacrifice Issac.