public void random(int level){
         if(level > 1){
             nextNode = new Expression(this.level-1, next);
             nextNode2 = new Expression(this.level-1, next);
         }
         else{
             double ran = (Math.random());
             nextNode = new InputXY(ran);
             nextNode2 = new InputXY(ran);
         }
     }