Create an Azure AD security group for each business unit and assign the respective business unit security role to each group team.
- Create a user in Microsoft Azure AD
- Login to portal.office.com.
- Navigate to Admin->Teams&groups->Security tab
- Click on Add a Group, Give a group name and description.
- Click on Create Group
- The group is now created.
- Now, all users who belong to this security group will have access to this Business Unit with assigned security role.