INSERT INTO parent_of (id, parent_id, isdir, name)
VALUES (1, NULL, 1, 'root')
     , (2, 1, 0, 'file1')
     , (3, 1, 1, 'dir1')
     , (4, 1, 0, 'file2')
     , (5, 1, 1, 'dir2')
     , (6, 5, 0, 'file3')
     , (8, 7, 0, 'file4'); -- last one is orphan

INSERT INTO parent_of VALUES (7, 5, 1, 'dir3'); -- orphan is resolved