Hello @roogem ,
you should be able to configure the physical ports as an 802.1Q trunk carrying vlan 10 and vlan 20.
What Network OS is running on the device?
ASA software or FTD software ?
What do you see for configuration ?
ASDM for ASA SW , FDM for FTD ?
the type of NOS makes some difference on how the device operates.
Hope to help
Giuseppe