Hi Sindhu,
You can use Calculated field to group those under first n months and then display using filter or color shelf.
1. First create a calculated field,
2. Add year in the filter shelf to view only that years details.
3.Create N value as a parameter.
4. Now enter N value and add the created calculated field in color shelf to view details. (below shown for N = 1, 3)
Hope this helps you.