not clear about your question. but something must be made clear.
The domain in Call DrillDown(domain, level+1, bu) should be referenced to TGRMain, Groups, Headings according to your code.
According to your code, there is one assumption: Click on the first level links(Page("TGRMain")) will navigate to the second level(Page("Groups")), and click on second level links will navigate to the third level(Page("Headings"))
The domain in Call DrillDown(domain, level+1, bu) should be referenced to TGRMain, Groups, Headings according to your code.
According to your code, there is one assumption: Click on the first level links(Page("TGRMain")) will navigate to the second level(Page("Groups")), and click on second level links will navigate to the third level(Page("Headings"))