How to add Arraylist items to Data table Column?

Hi all,
I have Data table Populated from database  with Column Month which contains values  .
and i have an other Array list which contains the Months from 1 to 12.
Now i have to insert the missing months into Data table from Arraylist.
Any Idea how i do that because i have to shown the 12 months on report .
 
Best Regards
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