True artist`s/scientist`s/any-person-who-cultivates-themself`s path is always a beginning.

I like the green colours, although some more hue shifting wouldn`t harm. Colouring trees is always a relative thing, because colours depend on ambience so much, and drawing trees without ambience is kinda pointless, imo. In addition, you mentioned videogames, so if this tree is taken from some sketch you should show it for us to see what you are aiming at, what your style is in general.
The shading of the stem is quite strange for me in the upper part: it looks a bit like the tree is twisted, but at the same time it looks rather flat.
The foliage lighting/shading makes it looks too shiny, like if the tree was made of glass/plastic. The overall shape is really... specific. I can`t comment on that, especially without seeing the ambience style, as mentioned.
So, as I see it, it should be first decided in which place and time the tree is situated before startig to work on lighting-colouring; only shape can be set before that moment. What time of day is it? What is the weather like? May be there is a little morning mist or something? May be the tree stands near water which tends to reflect light and create an additional light source? There are millions of ways to influence on colours, and you should know which ones you are going to implement before messing with the palette.
