[{cards:{starter:[],intermediate:[],advanced:[{cards:[{cardTitle:"this card is for you",performance:[],cardID:32,}],unit:3/** this is the unit we want to push our new card object into*/}]},firstName:"Sepideh",email:"sepideh@example.com",}]

db.collection.update({email:"sepideh@example.com","cards.advanced.unit":3},{$push:{"cards.advanced.$.cards":{cardTitle:"this card is for me",performance:[],cardID:33}}})