Hi Pallavi,
If you need to display your data as hierarchy at report level. note that such functionality is only available with OLAP data with hierarchies.
but you can play with formatting of a table to make it look like a hierarchy.
Please refer following link for more details.http://scn.sap.com/community/businessobjects-web-intelligence/blog/2013/06/05/bobj-trick-to-display-table-data-in-hierarchy-format
But If you need to use only power of drilling functions then go for custom hierarchies/custom navigation paths as suggested by others in above comments.
Note: Custom Navigation path does not display day in hierarchy form but allows you to navigate through hierarchy using drilling options.