def add_child( Hash options is optional, Tree *children )
    # Subroutine body here
end

##</code><code>##

def add_child( *children )
    options = children[0].is_a( 'Hash' ) ? children.shift : Hash.new;
    if children.any? { |node| !node.is_a( 'Tree' ) }:
        raise ArgumentError "Non-Tree argument found in add_child()"
    end

    # Resume regular processing here
end