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God did create the "tree of the knowledge of good and evil". Genesis 2:9.
God commanded our first parents not to eat of the tree of the knowledge of good and evil. This was a simple test of their loyalty and faith in God. The tree of the knowledge of good and evil was necessary for this purpose.
You are correct. The Bible doesn't tell us what kind of fruit it was. That is not relevant. It could have been an apple. It probably wasn't but it doesn't matter. As soon as God placed a commandment on that tree - DO NOT EAT OF IT! - it BECAME the tree of the knowledge of good and evil.
Adam and Eve would have gained the knowledge of the difference between good and evil whether they ate of the tree or not. The actual eating of the fruit was not the most important thing. It was the choice they would make that was crucial.
In their decision was bound up the issues of eternal life or death. As soon as they chose, they would know the difference between good and evil. As it turned out, they made the wrong decision and then they ate of the tree.
Access to the tree of life, for the sons and daughters of Adam, including you and me, has always been contingent on our decisions when confronted with a choice between good and evil. Let's not repeat the mistake of our first parents!