Parse the xml tree into ArTree objects.

def fill_tree_from_xml(tag, ar_tree, namespace):
    # type: (_Element, ArTree, str) -> None
    """Parse the xml tree into ArTree objects."""
    for child in tag:  # type: _Element
        name_elem = child.find('./' + namespace + 'SHORT-NAME')
        # long_name = child.find('./' + namespace + 'LONG-NAME')
        if name_elem is not None and child is not None:
            fill_tree_from_xml(child, ar_tree.append_child(name_elem.text, child), namespace)
        if name_elem is None and child is not None:
            fill_tree_from_xml(child, ar_tree, namespace)