Sub addRow()
Dim lRow As Long, lLastR As Long
Dim k As Long, arrInf, i As Long

Application.ScreenUpdating = False

lLastR = Cells(Rows.Count, 1).End(xlUp).Row
For lRow = lLastR To 2 Step -1
    k = InStr(1, Cells(lRow, "M"), ",")
    If k > 0 Then
        arrInf = Split(Cells(lRow, "M"), ",")
        k = UBound(arrInf)
        Range("A" & lRow & ":N" & lRow).Copy
        Range("A" & lRow & ":N" & lRow).Resize(k, 1).Insert Shift:=xlDown
            For i = 0 To k
                Cells(lRow + i, "M").Value = arrInf(i)
            Next i
    End If
Next lRow
Application.CutCopyMode = False
Application.ScreenUpdating = True
End Sub