function CustomSortProc(Node1, Node2: TTreeNode; Data: Longint): Integer; stdcall;
begin
  if Data = 0 then
    Result:= System.AnsiStrings.AnsiStrIComp(PAnsiChar(AnsiString(Node1.Text)),
      PAnsiChar(AnsiString(Node2.Text)))
  else
    Result:= -System.AnsiStrings.AnsiStrIComp(PAnsiChar(AnsiString(Node1.Text)),
      PAnsiChar(AnsiString(Node2.Text)));
end;

Node.CustomSort(@CustomSortProc, 0);