Sentence:  Money does not grow on trees. There is no <WSD>money tree</WSD> at Mount Kildare. If we had a <WSD>money tree</WSD>, boys, there would be no need of the bakery, no need of the raffle. 
Meaning of the word marked with <WSD> tags:  An imaginary tree from which money can be plucked; "mentioned as an impossible object — see: money doesn't grow on trees".