Javascript Data Structure Tree Binary Tree

'use strict';/*from  w  ww.j a v a2 s . c om*/

class BinaryTree {
  constructor(data) {
    this.data = data || null;
  }

  leftBranch() {
    this.left = this.left || new BinaryTree();
  }

  rightBranch() {
    this.right = this.right || new BinaryTree();
  }

  insert(data) {
    if (this.data === null) {
      this.data = data;
    } else if (this.data > data) {
      this.leftBranch();
      this.left.insert(data);
    } else {
      this.rightBranch();
      this.right.insert(data);
    }
  }

  include(data) {
    if (this.data === data) {
      return true;
    } else if (this.data > data && this.left !== undefined) {
      return this.left.include(data);
    } else if (this.data < data && this.right !== undefined) {
      return this.right.include(data);
    } else {
      return false;
    }
  }

  all(allNodeData = []) {
    if (this.data) allNodeData.push(this.data);
    if (this.left) this.left.all(allNodeData);
    if (this.right) this.right.all(allNodeData);
    return allNodeData;
  }

  count() {
    return this.all().length;
  }
}

const tree = new BinaryTree;
tree.insert(8);
tree.insert(4);
tree.insert(12);
tree.insert(6);
console.log(tree.all());
console.log(`Tree Contains ${tree.count()} element(s)`);
console.log("Has 4?", tree.include(4));
console.log("Has 5?", tree.include(5));
console.log("Has 12?", tree.include(12));
console.log("Has 13?", tree.include(15));