Would just adding the totals and subtotals work? Right click on Category and Sub-Category on your rows shelf and check Subtotals. Then, you get the total for all the products within Sub-category so for Bookcases. Then, at the very bottom the total for Furniture will be shown for the overall total.
Hope this helps!
The above steps is not achieving my visualization as customer is willing to have display as excel file. I am using custom sql with UNION ALL for each level but still i am not able to achieve the visualization. but it is affecting report performance lot.
Do you have any idea which can be implemented in Tableau itself?