The game was enjoyable, but there were some issues.
One being that the the performance on the WebGL client suffered dramatically once you were somewhat fast. And also the draw distance is kind of short.
I know that if you increase the draw distance the performance will be even worse but it is unusual for the amount of vertices on screen for it to start dipping in fps this fast. Maybe you should look into enabling instancing on the materials used in the trees.
Another idea would be to use object pooling so you don't always instantiate new objects. I don't know how you set up your game but if you just create new gameobjects and destroy the unneeded ones once they are out of the screen this will greatly impact performance. By reusing your objects in form of pooling you can mitigate this loss in frames per second.
EDIT: I think I found out another major problem. If your trees are constructed out of individual Unity primitives and not a singular mesh you will also run into issues.
If you did it that way you should look into modelling your trees in an external program like Blender and export the model and use that instead of a bunch of primitives parented to each other.