I bought this inexpensive CCTV pin camera online.
the first step is to get a branch of a dead tree or from a garden clean up, big enough that you can fit in the camera.
using a'n xacto knife cut a square of the bark slightly bigger than the camera
using a router or a drill, start digging until you have a deep enough hole for the camera
use a small drill bit to open the hole for the lens
The dificult part is to drill the hole without going all the way through, but if yo do this you can always use some putty to diguise
Th hole for the wire was done the same way
All the measures depend on the size of the camera and the thikness of the branch