How to save a TGraph2D Object in a root file?

Hi all:
I create a TGraph2D* object “dt” by SetPoints,then i save it:
f ->Write();
dt ->Write();
(a root file has been open)
f is a TF2* object ,and it is saved successfully.
However the “dt” seem not saved successfully.
When i open the root file and use TBrowser, there is only a "Graph2D"icon but not “dt” icon.

The default name for a TGraph2D is “Graph2D”.
You should give a name via, eg