How do I create a new instance of a class from within a class method?

factory.coffee

class TreeNode
  constructor: (@tree, @id, @name, @data={}, @children=[]) ->
    @set_color() unless @data.$color
    @name = @id if !@name? or @name.blank()

  @create_root: (tree) ->  # acts as a TreeNode class method. Called like TreeNode.create_root(tree)
    new this tree, 'root' 
    
    # "new this" is incorrect and does not work.
    # I want to call the equivalent of "new VariationTreeNode(...)" or "new ProfileTreeNode(...)",
    # based on the class I call create_root on - eg: ProfileTreeNode.create_root(tree)

class VariationTreeNode extends TreeNode
  color: -> 'yellow'

class ProfileTreeNode extends TreeNode
  color: -> '#F44'

factory.js

// Compiled coffeescript
var ProfileTreeNode, TreeNode, VariationTreeNode;
var __hasProp = Object.prototype.hasOwnProperty, __extends = function(child, parent) {
  for (var key in parent) { if (__hasProp.call(parent, key)) child[key] = parent[key]; }
  function ctor() { this.constructor = child; }
  ctor.prototype = parent.prototype;
  child.prototype = new ctor;
  child.__super__ = parent.prototype;
  return child;
};
TreeNode = (function() {
  function TreeNode(tree, id, name, data, children) {
    this.tree = tree;
    this.id = id;
    this.name = name;
    this.data = data != null ? data : {};
    this.children = children != null ? children : [];
    if (!this.data.$color) {
      this.set_color();
    }
    if (!(this.name != null) || this.name.blank()) {
      this.name = this.id;
    }
  }
  TreeNode.create_root = function(tree) {
    return new this(tree, 'root');
  };
  return TreeNode;
})();
VariationTreeNode = (function() {
  __extends(VariationTreeNode, TreeNode);
  function VariationTreeNode() {
    VariationTreeNode.__super__.constructor.apply(this, arguments);
  }
  VariationTreeNode.prototype.color = function() {
    return 'yellow';
  };
  return VariationTreeNode;
})();
ProfileTreeNode = (function() {
  __extends(ProfileTreeNode, TreeNode);
  function ProfileTreeNode() {
    ProfileTreeNode.__super__.constructor.apply(this, arguments);
  }
  ProfileTreeNode.prototype.color = function() {
    return '#F44';
  };
  return ProfileTreeNode;
})();

simpler_working_example.coffee

class TreeNode
  constructor: ->
    alert "constructed with color #{@color()}"

  @create_root: ->
    new this()

class VariationTreeNode extends TreeNode
  color: -> 'yellow'

class ProfileTreeNode extends TreeNode
  color: -> '#F44'

ProfileTreeNode.create_root()