text: function Node(val) {
      this.value = val;
      this.left = null;
      this.right = null;
  }
  
  Node.prototype.visit = function () {
      if (this.left) this.left.visit();
      console.log('value:', this.value);
      if (this.right) this.right.visit();
  };
  
  Node.prototype.addNode = function (n) {
      if (n.value < this.value) {
          this.left === null ? (this.left = n) : this.left.addNode(n);
      } else if (n.value > this.value) {
          this.right === null ? (this.right = n) : this.right.addNode(n);
      }
  };
  