Creating Department Groups in a report

Hello!
I am trying to create custom department groups in one of my reports. For example. we have a department here called Production Team and another one named Sales Team. Both of these are part of the Market Division. We want to track sales volume within the Market Division. I don't want to create a new field for this, I just want it to appear in the report.
Hopefully someone knows how to do this! I feel silly- it seems like it should be easy enough.
Let me know, thank you!

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Karah Weber
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