I created a Master page (new.master) using notepad and uploaded to "_catalogs/masterpage" of site collection root. After some approve and publish process I am able to change the site Master to the new.master.
However when I click on Design Manager > step 4. edit Master page, I can only see Oslo and Seattle. Same problem for step 6. edit page layout. When I click build page layout, in the Master page selection there are only Oslo and Seattle.
When I browse to /_catalogs/masterpage/, I see the icons of Oslo and Seattle are different from my new.master. I checked all of them have same content type (i.e. Page layout). What kind of dinition I have missed for new.master?