def collapse_focussed(self):
        """
        Collapse currently focussed position; works only if the underlying
        tree allows it.
        """
        if implementsCollapseAPI(self._tree):
            w, focuspos = self.get_focus()
            self._tree.collapse(focuspos)
            self._walker.clear_cache()
            self.refresh()
Collapse currently focussed position; works only if the underlying
        tree allows it.