As for the existing feature suggestion mentioned by Hitsville:
As for your actual issue… If this is 2 sequential parts of the same video instead of different (quality) versions… you might need to review your file naming. Properly named, such stacked files will be displayed as a single item with the duration of all its parts, playing all those parts in sequence.
Example:
Movies <- the folder linked to your movie library
Die letzte Spur - Alexandra, 17 Jahre (2011)
Die letzte Spur - Alexandra, 17 Jahre (2011) - pt1.ext
Die letzte Spur - Alexandra, 17 Jahre (2011) - pt2.ext
