The 'Tree Of Knowledge' is an allegorical description of everything that could be known, including that stuff God didn't want us to know.. Since by definition humanity has lived outside of Eden since Adam and his missus were expelled for behaviour unbecoming, you can hardly claim the world we know is alien to us.
In fact, christianity has always had a difficult relationship with science simply because it's a religion that relies on ignorance, with priests supplying the wisdom to their congregations rather than society revealing all. After all, the story of the 'Tower of Babel' confirms this, as God inserts an obstacle to human progress by forcing them to speak in lots of languages instead of one, a clear recognition that communication spreads ideas, and ideas were not a good thing as far as the fixed messages of christianity were concerned. The initiative to translate the Bible into english so that every common man could read it not only threatened the social influence of the priesthoods, it sparked wars on religious differences, and encouraged colonial ventures to the new world to escape the restrictions of religious argument at home. Of course it has to underlined that the 'stuff God didn't want us to know' is never decided by God - it's always human beings who decide that.
These principles are further confused by the history of christianity in that we have to accept our current version is neither conformal nor the same as ancient texts, which were subject to censorship and rwrites. Indeed, the attempts to create a universal christian faith went hand in hand with censoprship, as valid ancient texts were either approved or discarded, and in any case, no version of the Bible contains a consistent account.
The 'apple' story is merely there to illustrate an aspect of undesirable female behaviour and a warning to restrain it.