Iterator that returns the constituency trees
        @rtype: L{Ctree}
        @return: iterator to all the constituency trees

def get_trees_as_list(self):
        """
        Iterator that returns the constituency trees
        @rtype: L{Ctree}
        @return: iterator to all the constituency trees
        """
        mytrees = []
        if self.constituency_layer is not None:
            for tree in self.constituency_layer.get_trees():
                mytrees.append(tree)
                return mytrees