I think the problem is you don't have multiple partitions for the Windows installation. You need an unencrypted Windows partition to begin the boot process so that it can ask for your Bitlocker password and decrypt the encrypted main Windows partition. Typically on a non-Apple Windows PC, there will be three (many times four) partitions on a Windows boot drive.....one is an ESP (aka EFI partition for the bootloader), a Windows boot/recovery partition, the main Windows partition, and possibly a backup partition or a partition from the OEM holding the original recovery software image provided by the manufacturer. For people installing Windows cleanly there are just three partitions. The "boot/recovery" partition is similar to the macOS recovery partition which is used to boot into a recovery mode so rescue & repair utilities can be accessed, and to allow booting an encrypted OS.
I did a quick search and it seems like it should be possible to use Bitlocker with Bootcamp (there are multiple posts & articles), but the majority of hits are about people having issues with Bitlocker (not your issue though).
Plus on a non-Apple Windows PC, the computer's firmware will have a TPM which is used to help manage a Bitlocker encrypted system, but macOS has no TPM....I have no idea whether Bootcamp has something to simulate its behavior since I don't use Bootcamp (or even Windows).