One to many from one table ( T-SQL )

 SELECT [F2].[Id], [F2].[Name], CONCAT([F2].[Size], 'KB') AS [Size]
    FROM Files AS [F]
    RIGHT JOIN Files AS [F2]
    ON [F].ParentId = [F2].Id
    WHERE [F].[Id] IS NULL
    ORDER BY [F2].[Id] ASC, [F2].[Name] ASC, [F2].[Size] DESC