Index of the Headings in the Table - Group row number 1. 1.1

I need to see the data as below in the grouping table

Index of the Headings in the Table.

1  Heading

1.1 Sub Heading

1.1.1 Detail Heading1

1.1.2 Detail Heading2

etc..

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kindly help me on the expression

ShanmugaRaj