Okay first of all we need to take into account the points that you didnt include. You are assuming that a tree is intelligently designed yet you are not taking into account certain factors such as time, genetic mutation, or a proper definition of complexity. Natural selection says that, given the right amount of time and circumstances, any matter(organic or non-organic) will eventually and indefinately evolve into a more complex state. As for complexity: a tree is a complex organism, but evolution can create any organism regardless of complexity, given the right circumstances and physical perimeters. As long as the circumstances are right, and as long as there is enough time and matter, then the complexity of any organism is irrelevent to the laws of physics. And the existence(curently theoretical) of a multiverse negates intelligent design. And you have some false facts which i will disprove; consciousness is not required to allow any form of biological function, look at viruses for instance. Also, a brain is not needed to pass down information through heredity. Ever heard of something called DNA?
So in summary, not only does evolution theory say that it is possible for a tree to form without the existence of a God, but what we percieve as complexity in organisms may not be anything more than the by-product of natural selection and parallel universes.