is it necessary to add sugar while making probiotic(fermenting) apple
Undesirable microbes are typically kept in check via sanitization of the equipment and the environment; sanitizers are distinct from cleaners (soap, washing soda) in that they kill microorganisms. You can either purchase sanitizers (e.g. Campden tablets, Star San etc), or roll your own antiseptic solution:


  "dilute 2 teaspoons of potassium or sodium metabisulfite and 2 teaspoons of malic, citric, or tartaric acid in 1 quart of water" — Claude Jolicoeur. "The New Cider Maker's Handbook"


(Disclaimer: I don't use any sanitizers in my mead production and only clean the glass jars and other equipment. This may result in a wilder range of flavors, though.)