How to add a network interface in lxc?

thank you very much ,but I have a new question.
if I create a container for the first time in host server ,there will be lxcbr0 and lxdbr0 bridge appear in host server ,and vet***1 will bridge in lxdbr0 auto.

if I create a new container ,there is no new bridge appear in the same time ,and the new vetch**2 will also bridge to lxdbr0 .

I want a new bridge will be created auto when I create a new container .

if I create a bridge by myself , is does not work rightly.

I need your help.