using DevExpress.Utils.Menu;
using DevExpress.XtraTreeList;
using DevExpress.XtraTreeList.Columns;
//...
private void treeList1_ShowTreeListMenu(object sender, DevExpress.XtraTreeList.TreeListMenuEventArgs e) {
   TreeListHitInfo hitInfo = treeList1.CalcHitInfo(e.Point);
   if(hitInfo.HitInfoType == HitInfoType.SummaryFooter)
      e.Menu.Items.Add(new DXMenuItem("Clear All", new EventHandler(this.clearAllMenuItemClick)));
}

private void clearAllMenuItemClick(object sender, EventArgs e) {
   foreach (TreeListColumn column in treeList1.Columns) 
      column.SummaryFooter = SummaryItemType.None;
}

Imports DevExpress.Utils.Menu
Imports DevExpress.XtraTreeList
Imports DevExpress.XtraTreeList.Columns
'...
Private Sub TreeList1_ShowTreeListMenu(ByVal sender As Object, 
ByVal e As DevExpress.XtraTreeList.TreeListMenuEventArgs) 
Handles TreeList1.ShowTreeListMenu
   Dim HitInfo As TreeListHitInfo = TreeList1.CalcHitInfo(e.Point)
   If HitInfo.HitInfoType = HitInfoType.SummaryFooter Then
      e.Menu.Items.Add(New DXMenuItem("Clear All", AddressOf Me.clearAllMenuItemClick))
   End If
End Sub

Private Sub clearAllMenuItemClick(ByVal sender As Object, ByVal e As EventArgs)
   Dim Column As TreeListColumn
   For Each Column In TreeList1.Columns
      Column.SummaryFooter = SummaryItemType.None
   Next
End Sub