def is_single_tree(data_wrapper):
db = data_wrapper.data_block<EOL>bad_ids = db[db[:, COLS.P] == -<NUM_LIT:1>][<NUM_LIT:1>:, COLS.ID]<EOL>return CheckResult(len(bad_ids) == <NUM_LIT:0>, bad_ids.tolist())<EOL>
Check that data forms a single tree

    Only the first point has ID of -1.

    Returns:
        CheckResult with result and list of IDs

    Note:
        This assumes no_missing_parents passed.