Yes you can have multiple varieties on one tree. Cocktail tree are usually not the best things to have . Multiple reasons one reason is cuz some varieties of some grow a lot faster than others .
And it happens to citrus a lot then you have this other issue if you don't know where the limb is grafted you accidentally cut it off .
That issue is mangoes there's so many different varieties that some people may like while others varieties they won't like .
With citrus they may add most popular citrus varieties naval orange , pineapple orange , Meyer lemon , eureka lemon , Persian lime , cara cara / red navel and murcott tangerine