public function getTrail()
{

    $parent = $this -> parent();

    $trail = array();

    while($parent !== NULL)
    {

        // push parent element to trail
        $trail[] = $parent;

        // go backwards one node
        $parent = $parent -> parent();

    }

    // you want trail in reverse order [from root to latest]
    return array_reverse($trail);

}

class TreeNode {
    /**
 * the parent node
 *
 * @var TreeNode
 */
    private $parentNode=null;
     /**
 * the children of this node
 *
 * @var TreeNode[]
 */
    private $children=array();
     /**
 * The user element this tree node holds.
 *
 * @var Object
 */
    private $element;
}

interface BreadcrumbInterface
{
    public function getLabel();

    public function getParent(); // returns an instance of BreadcrumbInterface, or null
}

abstract class BaseNode implements BreadcrumbInterface
{
    protected $parent = null;

    public function accept(BreadcrumbVisitor $visitor)
    {
        $visitor->visit($this);
    }

    public function setParent(BreadcrumbInterface $parent)
    {
        $this->parent = $parent;
    }

    public function getParent()
    {
        return $this->parent;
    }
}

class BreadcrumbVisitor
{
    protected $breadcrumbs = array();

    public function visit(BreadcrumbInterface $node)
    {
        $parent = $node->getParent();
        if ($parent instanceof BaseNode) {
            $parent->accept($this);
        }

        $this->breadcrumbs[] = $node->getLabel();
    }

    public function getBreadcrumbs()
    {
        return $this->breadcrumbs;
    }
}

$rootPage = new Page(/*...*/);

$parentPage = new Page(/*...*/);
$parentPage->setParent($rootPage); // In reality you most likely wouldn't be building this structure so explicitly. Each object only needs to know about it's direct parent

$currentPage = new Page(/*...*/);
$currentPage->setParent($parentPage);

$visitor = new BreadcrumbVisitor();
$currentPage->accept($visitor);
$breadcrumbs = $visitor->getBreadcrumbs(); // returns an array, where the first element is the root

// then you can implode with ' > ' if you want
$breadcumbString = implode(' > ', $breadcrumbs);