MPTtree, Hieararchical trees in a database table

[eluser]jojovem[/eluser]
I extracted the last version of codeigniter. Then i extracted all files included in the latest Preorder Nested Tree functions.

When i tried to execute:

Code:

<?php

class Tree extends CI_Controller
{

     public function index()
     {
        $this->load->model('mpttree');
     }
}


/* End of file tree.php */
/* Location: ./application/controllers/tree.php */

?>

I got the error:
Fatal error: Class 'Model' not found in D:\Server\ci\application\models\mpttree.php on line 143

Then i changed de line 143
FROM:
class MPTtree extends Model{
TO:
class MPTtree extends CI_Model{

Then the error changed to:
Fatal error: Call to undefined method CI_Model::model() in D:\Server\ci\application\models\mpttree.php on line 192

And this one i cant fix it. Can anybody help me?

191 function MPTtree(){
192 parent::model();
193 }