method Columns.Add (ColumnCaption as String)

Adds a Column object to the collection and returns a reference to the newly created object.

TypeDescription
ColumnCaption as String A string expression that indicates the caption for the column being added
ReturnDescription
VariantA Column object that indicates the newly added column.

The AddColumn event is fired when a new columns is added to Columns collection. Use the Caption property to change the column's caption. 

The following sample shows how to add columns to your group based on a recordset:

With ExplorerTree1
    With .Groups.Add("Group 1")
        Set rs = CreateObject("ADODB.Recordset")
        rs.Open "Orders", "Provider=Microsoft.Jet.OLEDB.3.51;Data Source= D:\Program Files\Microsoft Visual Studio\VB98\NWIND.MDB", 3 ' Opens the table using static mode
        .BeginUpdate
            .ColumnAutoResize = False
            ' Add the columns
            With .Columns
                For Each f In rs.Fields
                    .Add f.Name
                Next
            End With
            ' Adds items
            .PutItems rs.getRows()
        .EndUpdate
    End With
End With