If you want to create textures of trees, just move to Zlín!
Masking cant be easier if trees are placed in front of an omnipresent orange walls:
You only have to wait for cloudy weather to avoid sharp shadows and need some high resolution camera with good image quality (DSLR, Micro 4/3… definitely not a mobile phone).
Then you just erase the wall in an image editor (by selecting it’s color, creating a mask from the selection and using some additional tools like Refine Edge in PhotoShop).
Quick in-game test:
