Minecraft wiki entry for Trading, associated text: Only one item is offered (e.g. wandering trader cannot sell both cocoa beans and pink dye). Each group of single-offer trades has the same chance to be chosen as a normal trade based on weight. For example, each individual sapling does have the same chance of being offered as a slimeball, because the sapling group as a whole which consist of 4 items and has 4 weight (multiple sapling cannot be offered however).