You will have to work on this but here's a starting point
Sub merge_em()
Dim L As Long
Dim opres As Presentation
Dim fd As FileDialog
Set opres = Presentations.Add
Set fd = Application.FileDialog(msoFileDialogOpen)
With fd
' change to point to your folder
' you may need to chasnge the vioew type to large icons
.InitialFileName = Environ("USERPROFILE") & "\Desktop\TP Docs"
.ButtonName = "Merge"
.AllowMultiSelect = True
.Filters.Clear
.Filters.Add "Presentations", "*.pptx"
If .Show = True Then
If .SelectedItems.Count > 0 Then
For L = 1 To .SelectedItems.Count
Call opres.Slides.InsertFromFile(.SelectedItems(L), opres.Slides.Count)
Next L
End If
End If
End With
End Sub