{
Parent, GetNextChild, GetPrevChild example
The following code tests to see if the currently selected item has a sibling; if so, HasSibling will be set to true.
} 
var
  HasSibling: Boolean;
  SelNode: TTreeNode;
  ParentNode: TTreeNode;
begin
  SelNode := TTreeView1.Selected;
  ParentNode := SelNode.Parent;
  HasSibling := (ParentNode.GetPrevChild(SelNode) <> nil) or 
                (ParentNode.GetNextChild(SelNode) <> nil);
end; 
