What are the differences between the -next tree and the -mm tree?

[Hao Lee]

Hi,

I'm sorry to bother you to ask some questions about -next tree and -mm tree.
I have read some documents about kernel trees, but I don't know the
difference between the -next tree and -mm tree.

In this post:
http://lists.kernelnewbies.org/pipermail/kernelnewbies/2013-October/009145.html
It seems that the -mm tree has been substituted by the -next tree.

Besides, I can't find -mm tree in anywhere.
So, could you explain the difference between the two trees.

Regards,
HaoLee