Have you ever read the ingredients in fruit cake?
People might think it's healthy because it contains the word fruit in it but don't kid yourself...fruit cake is cake just like regular chocolate cake.
It'll make you gain weight for sure...but not the kind of weight you want to gain. It'll just make you fat.
Base your diet around single ingredient unprocessed foods. If you are trying to gain weight, then use calorie dense foods like whole eggs, grass fed beef, natural almond butter etc.