Why did God create the devil and also the tree that would make us all fall?

I know the devil used to be an angel and then tried to take over heaven so God banished him but being that God is all knowing why create him them? Wouldnt it have been better to not create him in the first place? Just like why make the tree that caused adam and eve to sin? why not put the tree somewhere they would not find it or even better not even create it?