Here are the images regarding the tree background
Please advise
I did finally use Custom Renderworks with a full Black background with Lit Fog @ 35% Smooth and the Mostly Sunny HDRI, but using the Lighting from the HDRI Sky39
All options selected, Image exposure = 100%, All Quality set to High, Max Reflections = 3.
Lighting Options : Indirect Lighting = None, Ambient Info = OFF, Emitter Brightness = 100%, Color Temp = 2800K, Enviroment Light from other background - Sky-39