Add an "or" to the filter options in reports

We are assigning projects to the department that does the most work on them. I also created a second field to track departments who will also do some work on them. 

• Department (main department that does most of the work)
• Associated Department (I created this field, as a multi-selection field for departments, so that we can also show which departments will be involved in projects). 

The problem is that I can't filter by both (if Department = Infrastructure OR if AssociatedDepartment = Infrastructure)

I'd rather not start adding the main department into the AssociatedDepartment field as it is visually redundant and can be confusing to some.