Finding a subtree in a CakePHP Tree

In CakePHP, how do you select just a subtree in a model which actsAs tree?

I tried this, to find the tree headed by the item with label = "My Label"

$this->find("threaded", array(
    "conditions" => array(
        "label" => "My Label"

...however looking at the logs, it runs this SQL:

SELECT, Menu.parent_id, Menu.lft, Menu.rght, Menu.label,
FROM menus Menu
WHERE label = 'My Label'

Which obviously only selects the one node, and not all its children.