<?php
//controller code:
$stuff = $this->MainModel->MyTreeBehaviorModel->find('all', 
     array('fields' => array('whatever', 'lft', 'rght'), 'order' => 'lft ASC'));
$this->set('stuff', $stuff);
//view code
echo $tree->generate($stuff, array('model' => 'MyTreeBehaviorModel'));