Sub mySpit()
    Dim rr As Range
    On Error Resume Next
    Set rr = Intersect(Selection.Columns(1), ActiveSheet.UsedRange).Areas(1)
    On Error GoTo 0
    If rr Is Nothing Then Exit Sub
    
    Dim Application_Calculation As XlCalculation
    Application_Calculation = Application.Calculation
    Application.Calculation = xlCalculationManual
    
    Dim arr As Variant
    Dim ya As Long
    Dim ss As String
    Dim yr As Long
    For yr = rr.Rows.Count To 1 Step -1
        ss = rr.Cells(yr, 1).Value
        If ss <> "" Then
            arr = Split(ss, ",")
            If UBound(arr) > LBound(arr) Then
                For ya = UBound(arr) To LBound(arr) + 1 Step -1
                    rr.Cells(yr + 1, 1).EntireRow.Insert
                    rr.Cells(yr, 1).EntireRow.Copy rr.Cells(yr + 1, 1).EntireRow
                    rr.Cells(yr + 1, 1).Value = arr(ya)
                Next
                rr.Cells(yr, 1).Value = arr(ya)
            End If
        End If
    Next
    
    Application.Calculation = Application_Calculation
End Sub