Option Explicit

Sub show_groups()
    Dim GroupStart( 1  To  10 ) As Integer, PreviousLevel As Integer
    Dim rRow As Range, i As Integer

    PreviousLevel =  1 
    For Each rRow In UsedRange.Rows
        If rRow.OutlineLevel > PreviousLevel Then
            For i = PreviousLevel +  1  To rRow.OutlineLevel
                GroupStart(i) = rRow.Row
            Next
            PreviousLevel = rRow.OutlineLevel
        ElseIf rRow.OutlineLevel < PreviousLevel Then
            MsgBox "Rows " & GroupStart(PreviousLevel) & "-" & rRow.Row & " is a group of " & PreviousLevel & " level"
            PreviousLevel = rRow.OutlineLevel
        End If
    Next
End Sub