Filtering departments according to the specified business unit as defined in the Organization tree

Summary:

Filtering departments according to the specified business unit as defined in the Organization tree

Content (required):

We have a requirement to filter departments according to the specified business unit as defined in the Organization tree.

During the implementation phase, the customer has implemented the work structure using common reference data set and they have not used different reference data sets. Since all work structures are built using common set, currently they are unable to filter departments according to the specified business unit.

Customer is looking for work around to associate departments with Business unit. 

Any ideas or anybody has done similar requirement earlier, can please share your thoughts.