With a hot glue gun, join the two sides and close up the seam.
Cut a roof to the size of your liking.
While pressing the house down on to the roof, squeeze a generous amount of hot glue all the way around.
I always keep extra moss handy for pressing into the glue before it dries. It not only hides the glue, but gives the house a very "foresty" feel.
I like the hole in the bark that looks like a tiny window.
It just needs a door.
With added moss and wool flowers (of course!).