Python extract .msg attachments from .msg files

I have some .msg files and each file contains several .msg attachments.

My goal is to use python to extract those .msg attachments and save them into another folder.

Usually I use extract_msg package to extract attachments as below:

msg = extract_msg.Message(msgdir) # msgdir is the directory of .msg file
if msg.attachments:
    for att in msg.attachments:
        att.save(customPath=outputdir) # outputdir is the directory of output folder

But when I use such code to these .msg files, it will extract both the original msg file and attached msg files. But I only want to extract the original msg file but keep the attached msg files.

To clarify my point if I have the following msg file:

A.msg
-A's attachment1: B1.msg
    -B1's attachment1: C1.pdf
    -B1's attachment2: C2.txt
-A's attachment2: B2.msg

This is what I want:

Output Folder:
-B1.msg
-B2.msg

And this is what I have:

Output Folder:
-Folder B1:
    -C1.pdf
    -C2.txt
-Folder B2