STart by building your report with the details rows, then right-click the detail row in the row group panel below the main report design.
Do "Add Group" then "Parent Group". Choose the field that contains Buy/Sell and tick the "Add group header" option.
A new column will be added with the buy/sell field added. Delete this new column and then in the original column above instrument name, click the cell and choose the Buy/Sell field.
STart by building your report with the details rows, then right-click the detail row in the row group panel below the main report design.
Do "Add Group" then "Parent Group". Choose the field that contains Buy/Sell and tick the "Add group header" option.
A new column will be added with the buy/sell field added. Delete this new column and then in the original column above instrument name, click the cell and choose the Buy/Sell field.
This should give you what you want.