There's an alternate method to UNPIVOT using CROSS APPLY, you could read about it on the following link to understand the code I'm posting.

http://www.sqlservercentral.com/articles/CROSS+APPLY+VALUES+UNPIVOT/91234/

SELECT itemNoAS Item,

CatAS CatID,

SubCatAS SubCatID

FROM #Test

CROSS APPLY( VALUES

( Cat1, SubCat11),

( Cat2, SubCat21),

( Cat3, SubCat31))x( Cat, SubCat)

ORDER BY Cat, SubCat