show all months of a year and group by in the same time !!

i have   a report that i should show dates in a table grouped by Year as parent group and then by month name as a child group

as shown in this screenshot :

i want to show months that are not shown between the arrows !!

how can i show all months from the min date till the end date 

for ex: if the min date 12/5/2015 and the max 5/10/2015 

how can i show in the parent child group 5|6|7|8|9|10 respectively even if there is no dates in any month

any help would be appreciated 

thanks