Where can I find these amazing models in this screenshot?

This is the screenshot in discussion.

I am using this image for a scenic influence on a new map I am hoping to have published towards the end of this month- However, I cannot find out how they have achieved these amazing orange/red trees.
I have attempted to find custom models online; to no success.

I have gone through all the models in my hammer (tf & other files), yet cannot find it to no avail. I am presuming they have got a custom white tree model, then coloured in the leaves different? But even so, it doesn't appear like there is any leave models within hammer itself. Slightly confused, but *any* help would be greatly appreciated.

Thanks in advance!
~ Niall

 

If I recall correctly, the trees in the Frontline Supply Drop have different skins for orange leaves, it might be those.

 

These are indeed the birch trees from Frontline!

 

Ayyy thanks guys~ really helped me there.