Network question (additional bridge)

Hi,
ucs is configured to use a bridge (br0)as primary interface; the hardware interface used is enp0s31f6.
Now i need an additional bridge which uses vlan. If using /etc/network/interfaces i would configure it like this:

# NEU: Virtuelles VLAN 99 Interface auf der physischen Karte
auto enp3s0.99
iface enp3s0.99 inet manual

# NEU: Bridge 99
auto br99
iface br99 inet manual
    bridge_ports enp3s0.99
    bridge_stp off
    bridge_fd 0

How do i configure this in the webinterface? I can select vlan when adding a network device but the dropdown only list br0 as underlying interface, not enp3s0

If i cant confiure this in the GUI is there a way via cli?

Thanks,
Christian