The tree in the yard, that staple of solidity, reality and undeniable fact is sometimes referred to as unreal by the Vedantin. What can he mean?
Essentially the rope/snake analogy is being flaunted and asked to do a great deal of work. We need to pull back a little further to get better focus and ask what the paradigmatic form of error is for the Vedantin. It is confusion or taking something to be that which it is not. That is perfectly fine for the everyday physical world. In poor light we take the stump to be a man, the piece of shell to be silver etc., etc.
That sort of talk does not translate/transfer to the metaphysical however. The tree is real but we may ask wherein does its perceptuality arise ? How does that out there physical reality come to be in my consciousness as it actually is. The short cut answer without going into the technicalities of upadhi and vritti is that there is a unity of the substratum of consciousness, a unity of Being. What is real on the physical side, a tree that is separate and real for the perceiver is unified on the metaphysical side. Taking the physical to be the only reality is a mis-take. This is the world of duality. Keeping both sides going is the world of non-duality.
Thus we get the extravagant closing down sale of the world: everything must go. This is an unreal bargain.