问不对每个输入进行排序的二进制搜索树添加方法- JavaScript

EN

function Node(data){
this.data=data;
this.left=null;
this.right=null;}

function BinarySearchTree(){
this.root = null;
var current=null;
var newNode=null;

this.add = function(data){
    var root = this.root;
        if(!root){
            this.root= new Node(data);
            return;
        }else{
            if(this.ifExists(data)){
            }else{
                current=root;
                newNode= new Node(data);

                while(current){
                    if(data<current.data){
                        if(!current.left){
                                current.left=newNode;
                            break;
                        }else{
                                current= current.left;
                             }
                    }else{
                        if(!current.right){
                                current.right=newNode;
                            break;
                        }else{
                                current=current.right;
                            }
                        }
                    }
                }
            }
        }
}
this.ifExists=function(data){
         var current = this.root;
//       console.log(current);
         while(current){
             if(data==current.data){
                 return true;
             }
             current = data < current.value ? current.left : current.right;
         }
         return false;
     }
}

var bst= new BinarySearchTree();
bst.add(7);
bst.add(8);
bst.add(4);
bst.add(1);
bst.add(15);
bst.add(67);
bst.add(9);
bst.add(3);
console.log(bst);