Tree Creator Shader will not fade

How can I have a tree made with Tree Creator (with Tree Creator Shaders) slowly fade over the course of a scene? I am not sure how to change the rendering setting of the tree so that changes in its alpha value will make it transparent.

I am calling the following code in update:

 GameObject tree= GameObject.FindGameObjectWithTag("largeTree");
 Color color = tree.GetComponent<Renderer>().material.color;
 color.a -= 0.1f;
 tree.GetComponent<Renderer>().material.SetColor ("_Color", color);

My tree currently has "Nature/Tree Creator Bark" and "Nature/Tree Creator Leaves" Shaders. I tried making the Tree Shader Standard and changing its render setting to Transparent, but this resulted in errors and still would not allow the tree's transparency to be changed.