How to group rows without it being based on a column key?

I want to group rows based on certain fields in rows without those fields being used as columns in the grid.

For e.g in [this](https://codesandbox.io/s/group-million-test-9d7er?file=/src/Grid.js) I want to group by row field country & year but I don't want the country & year to be a part of the columns and take up space.

This was possible in earlier data-grid versions that you can check [here](https://codesandbox.io/s/rdg-grouping-forked-esjg0?file=/src/index.js).

What I need it to look like is shown below, here the multilevel grouping is taking place in 1 column but if we want to do that in react-data-grid currently it will occupy multiple columns to achieve the same result.


Workarounds that I can think of for this might be if we can reduce the column width to be small and then for the rows where grouping happens we use column-span to take the rest of the space in the row for the group label? Not sure how to implement this though.