Tablix Group Properties Dialog Box, Advanced
Select Advanced on the Tablix Group Properties dialog box to set labels for the document map and set the parent field in a recursive hierarchy group.
Type or select a label or an expression that evaluates to a label. Click the Expression (fx) button to edit the expression. The value of the label appears on the document map. This option applies only to tables, matrixes, and lists.
Type or select a field as the parent field to group on, to create a recursive hierarchy group.