You cannot imply a hierarchical relationship between excel worksheets. Each
one is independent. What you can do is use a naming convention or a color
scheme to relate them. You main worksheet can be Data and the ‘sub’
worksheets could be s1Data, s2Data, s3Data. If you wanted subs to the subs,
say s1Data, that could become s1s1Data, s1s2Data, ect.