How to use nested list?

[OOXX1248]

Hello,I have a trouble to make a nested list.
The code is :
temp = ezodf.newdoc("odt","")
a = ezodf.List()
b = ezodf.List()
a.append(ezodf.ListItem('1'))
b.append(ezodf.ListItem('2'))
a += b
temp.saveas("temp.odt")

And i load the file(temp.odt) with Openoffice4.1.2 , (python3.4 ,win10 64bit environment)
Openoffice only shows the "a" list in the document, i feel frustrated about the situation.
Did i misunderstand something about the module or the function?
Please let me know.

At the end, thanks for the efforts what you devoted.It saves my time.