For more details regarding this recipe, refer to the following links:
- SUMMARIZE: https://docs.microsoft.com/en-us/dax/summarize-function-dax
- GROUPBY: https://docs.microsoft.com/en-us/dax/groupby-function-dax
- Nested grouping using GROUPBY versus SUMMARIZE: https://www.sqlbi.com/articles/nested-grouping-using-groupby-vs-summarize/