"merge cells" does not work

Hi,

I have 2 dimensions("Month/Year" and "Country")and a measure element.

I do not see lots of same month/year, repetition of dimension cells.( as I showed  blue colored areas in the table above)

I cannot merge cells because one  dimension ("Month/Year") corresponds to one dimension ("Country") again. Because of  structure of dimension (one to one) , it is impossible to merge same  "Month/Year" cells.

So, How can I simpfy the Month/Year dimension like this:

Please, help.

Thanks in advance.