property Items.ItemDivider(Item as HITEM) as Long
Specifies whether the item acts like a divider item. The value indicates the index of column used to define the divider's title.

Item as HITEM A long expression that indicates the item's handle.
Long A long expression that indicates the column's index.
A divider item uses the item's client area to display a single cell. The ItemDivider property specifies the index of the cell being displayed. In other words, the divider item merges the item cells into a single cell. Use the ItemDividerLine property to define the line that a divider item paints. Use the LockedItemCount property to lock items on the top or bottom side of the control.

The following sample adds a divider item that's locked to the top side of the first group in the control: ( Before running this sample please make sure that your control contains groups objects ):

With ExplorerTree1.Groups(0)
    .DrawGridLines = exNoLines
    With .Items
        .LockedItemCount(TopAlignment) = 1
        Dim h As HITEM
        h = .LockedItem(TopAlignment, 0)
        .ItemDivider(h) = 0
        .ItemHeight(h) = 24
        .CellCaption(h, 0) = "<b>Total</b>: $12.344.233"
        .CellCaptionFormat(h, 0) = exHTML
        .CellHAlignment(h, 0) = RightAlignment
    End With
End With