Delphi custom TTreeNode

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type
  TCustomTreeNode = class(TTreeNode)
  protected
    procedure Assign(Source: TPersistent); override;
  public
    Comment: string;
  end;

procedure TCustomTreeNode.Assign(Source: TPersistent);
begin
  if Source is TCustomTreeNode then
    Comment := TCustomTreeNode(Source).Comment;
  inherited;
end;


procedure TForm1.FormCreate(Sender: TObject);
var
  NewNode: TCustomTreeNode;
begin
  NewNode := TreeView1.Items.Add(nil, 'Node1') as TCustomTreeNode;
  NewNode.Comment := 'A comment';
  NewNode := TreeView1.Items.Add(nil, 'Node2') as TCustomTreeNode;
  NewNode.Comment := 'Another comment';
end;

procedure TForm1.TreeView1Click(Sender: TObject);
var
  Node: TCustomTreeNode;
begin
  Node := TreeView1.Selected as TCustomTreeNode;
  if Assigned(Node) then
    ShowMessage(Node.Comment);
end;

procedure TForm1.TreeView1CreateNodeClass(Sender: TCustomTreeView; var NodeClass: TTreeNodeClass);
begin
  NodeClass := TCustomTreeNode;
end;