VHDX and Bitlocker: please help me understand !

[irob]

Hello,
I have setup Windows USB.
I have now 2 drives one is called c: and the second one is D: which contains the Win2USB.VHDS file.
I also setup Bitlocker (in case I lose the USB stick) .
My question is this:
is the VHDS file encrypted?
When I go to Bitlocker manager is tells me that C: is encrypted but d: is not.
Can anyone explain it to me?
Thanks
iR