var assert = require('assert');

​

function Node(val) {

  this.val = val;

  this.left = this.right = null;

}

​

function mergeTwoBinaryTrees(tree1, tree2) {

  // Fill in this method

  return tree1;

}

​

function Node(val) {

  this.val = val;

  this.left = null;

  this.right = null;

}

​

// Regular binary trees

var tree1 = new Node(4);

tree1.left = new Node(1);

tree1.right = new Node(3);

​

var tree2 = new Node(5);

tree2.left = new Node(10);

tree2.left.left = new Node(17);

tree2.left.right = new Node(3);