protected function getDisplayTree()
    {
        $display_tree = new SwatTreeFlydownNode(null, 'root');
        if ($this->show_blank) {
            $display_tree->addChild(
                new SwatTreeFlydownNode(null, $this->blank_title)
            );
        }

        foreach ($this->tree->getChildren() as $child) {
            $this->buildDisplayTree($child, $display_tree);
        }

        return $display_tree;
    }