composite.js

var Item = function (obj) {
  this.children = [];
  _.extend(this, obj);
};

var p = Item.prototype;

p.add = function (obj) {
  this.children.push(new Item(obj));
  return _.last(this.children);
};

p.each = function () {
  var args = [].slice.call(arguments);
      args.unshift(this.children);

  return _.each.apply(_, args);
};

var root = new Item({
 id : 102031,
 name : 'root cause'
});

root.add({
  id : 456432,
  name : 'leaf'
}).add({
  id : 654644,
  name : 'leaf leaf'
});