VBA Grouping Concatenate best way to handle, based on data in column

Hi all,
I have been working on a grouping of data in Column A based on data in column D. if the data in Column D matches next row in D then Concatenate data in column A and delete that line

any help appreciated to steer me in right direction
thanks regards Peter

Data Sample.jpg




My code so far

Sub CommandButton2_Click()
Dim x               As Integer
Dim MyTimer         As Double
x = MsgBox("This with now Group all Data IN Column A and Sheet1!", vbOKCancel)
If x = 2 Then Exit Sub
If x = 1 Then
MsgBox (" Application.EnableEvents = False")
 'Application.EnableEvents = False
 
     Dim Lastrow As Long, r As Long
    Application.ScreenUpdating = False
    Lastrow = Range("A" & Rows.Count).End(xlUp).Row
  
  'status bar code loop
   ' For j = 1 To 50
    
    For r = Lastrow To 2 Step -1
        If Range("D" & r).Value = Range("D" & r - 1).Value Then
            Range("A" & r).Value = Range("A" & r - 1).Value & "_" & Range("A" & r).Value
            Rows(r).Delete xlShiftUp
        
        End If
        'status bar code line under
        ' Application.StatusBar = "Progress: " & r & " of " & Lastrow & ": " & Format(r / Lastrow, "0%")
    Next r
 
    ActiveSheet.UsedRange.Columns.AutoFit
    Application.ScreenUpdating = True
    Application.EnableEvents = True
    Application.StatusBar = False
 
 
 End If
 
 End Sub