var root1 = new Tree(1);
     // console.log(root1);
     var branch2 = root1.addChild(2);
     var branch3 = root1.addChild(3);
     var leaf4 = branch2.addChild(4);
     var leaf5 = branch2.addChild(5);
     var leaf6 = branch3.addChild(6);
     var leaf7 = branch3.addChild(7);
        var newTree = root1.map(function (value) {
     return value * 2;
    })
   console.log(newTree.value) // 2
    console.log(newTree.children[0].value) // 4
    console.log(newTree.children[1].value) // 6
    console.log(newTree.children[0].children[1].value) // 10
    console.log(newTree.children[1].children[1].value) // 14

Tree.prototype.map = function (callback) {
  // return a new tree with the same structure as `this`, with values generated by the callback
  var mapped = new Tree(this.value);
  mapped.value = callback(this.value);
  mapped.children = this.children;

  if (mapped.children.length === 0) {
    return mapped;
  }

  for (var i = 0; i < mapped.children.length; i++) {
    mapped.children[i].value = callback(mapped.children[i].value);
  };

  return mapped;

};

 var root1 = new Tree(1);
     // console.log(root1);
     var branch2 = root1.addChild(2);
     var branch3 = root1.addChild(3);
     var leaf4 = branch2.addChild(4);
     var leaf5 = branch2.addChild(5);
     var leaf6 = branch3.addChild(6);
     var leaf7 = branch3.addChild(7);
        var newTree = root1.map(function (value) {
     return value * 2;
    })
   console.log(newTree.value) // 2 --> my functions for this
    console.log(newTree.children[0].value) // 4 --> my function works for this
    console.log(newTree.children[1].value) // 6 ---> my function works
    console.log(newTree.children[0].children[1].value) // 10 ---> doesn't work
    console.log(newTree.children[1].children[1].value) // 14 ---> doesn't work