Remove unwanted object of image in MATLAB?
What you are asking is probably hopeless.

There are two quite difficult aspects:


detecting the trees that you want to remove. Given the very poor contrast, this will be hard to achieve by automated means. You need to implement some image segmentation method, then select the regions corresponding to the trees.
reconstructing the background image under the occluded parts. This is called image inpainting and requires sophisticated approaches.


All of this is highly technical and the standard tools in Matlab will probably not suffice.

If you just have one image to process, photoshopping will be much more efficient.