Методы Assign и AssignTo написаны для типов TStrings и TListItems

Автор: Максим Игнатьев

procedure TNamedHCollection.AssignTo(Dest: TPersistent);
var
  i, c: integer;
  TN: TTreeNode;
begin
  ...
    // Заветное решение для дерева.
  if Dest is TTreeNodes then
    with TTreeNodes(Dest) do
    begin
      BeginUpdate;
      Clear;
      for i := 0 to Self.Count - 1 do
      begin
        TN := AddChild(nil, Items[i].Name);
        TN.Assign(Items[i].Items);
      end;
      EndUpdate;
      exit;
    end;
  if Dest is TTreeNode then
    with TTreeNode(Dest) do
    begin
      for i := 0 to Self.Count - 1 do
      begin
        TN := Owner.AddChild(TTreeNode(Dest), Items[i].Name);
        TN.Assign(Items[i].Items);
      end;
      exit;
    end;
  inherited;
end;

procedure TNamedHCollection.Assign(Source: TPersistent);
var
  i: integer;
  FItem: TNamedHCollectionItem;
  TN, NN: TTreeNode;
begin
  .....
    // Заветное решение для дерева.
  if Source is TTreeNodes then
  begin
    Assign(TTreeNodes(Source).GetFirstNode);
    exit;
  end;
  if Source is TTreeNode then
  begin
    TN := TTreeNode(Source);
    while TN <> nil do
    begin
      FItem := Self.Add;
      FItem.Name := TN.Text;
      NN := TN.GetFirstChild;
      if Assigned(NN) then
        FItem.Items.Assign(NN);
      TN := TN.getNextSibling;
    end;
    exit;
  end;
  inherited;
end;