What I typically do is have a repeater for all the posts ordered by newest and only show for "cms.blog and cms.blogpost" doc types. This is typically the out of the box one on the "Blog" template. Then I'll place another repeater on the template and set it to only show for "cms.blogmonth" doc types. You can leave your path blank as it will automatically pick up all doc types below in the tree. Then set a transformation and such and you'll be set.