Git: move repository to a subfolder of another repository

It isn't done in BitBucket, it's done using git. You need the following steps:

• Fetch repo B into a cloned repo A. Git might warn you about this, but still do it.
• Checkout that fetched code (you will have only code from repo B at that moment) and move it all into a subfolder you want. Commit that.
• Checkout your repo A code again and merge the commit you have just created.

To merge a Repo B into Repo A as a subfolder, run this command inside Repo A;

git subtree add -P <prefix> <repo> <rev>

Set <prefix> to the name of the subdirectory, <repo> to the clone URL of Repo B, and <rev> to the revision of Repo B you want (HEAD if latest)

This will take the history of Repo B and merge it with Repo A, along with an additional merge commit.