procedure TForm1.FormCreate(Sender: TObject);
var i: integer;
   Node: TTreeNode;
begin

  Node := Form1.TreeView1.Items.AddChild(nil, 'C:\');
  Node.HasChildren := true;
  //TreeView1.OnClick:=@GetDir;
  GetDir(Node);
  TreeView1.Items.EndUpdate;

end;

procedure TForm1.GetDir(ParentNode: TTreeNode);
var
  sr: TSearchRec;
  node: TTreeNode;
  path: string;
begin
  node := ParentNode;
  path := '';
  Caption := node.Text;
  repeat
    path := IncludeTrailingPathDelimiter(node.Text) + path;
    node := node.Parent;
  until node = nil;
  //ShowMessage(path);

  // Сначала ищем папки
  if FindFirstUTF8(path + '*.*', faDirectory, sr) = 0 then
  try
    repeat
      if (sr.Name = '.') or (sr.Name = '..') or
         (sr.Attr and faDirectory <> faDirectory) then Continue;

      // Нашли Folder - вызываем рекурсивно GetDir
      node := TreeView1.Items.AddChild(ParentNode, IncludeTrailingPathDelimiter(sr.Name));
      //GetDir(node);
    until FindNextUTF8(sr) <> 0;
  finally
    FindCloseUTF8(sr);
  end;

  // теперь - файлы
  if FindFirstUTF8(path + '*.*', faAnyFile, sr) = 0 then
  try
    repeat
      if (sr.Name = '.') or (sr.Name = '..') or
         (sr.Attr and faDirectory = faDirectory) then Continue;

      // Нашли файл - просто добавляем его в дерево
      TreeView1.Items.AddChild(ParentNode, sr.Name);
    until FindNextUTF8(sr) <> 0;
  finally
    FindCloseUTF8(sr);
  end;
end;