Every assumption entails a conclusion. Assumptions are starting points, basic givens, points of view, premises, what have you. Yes, I begin by having concluded that the words of Genesis are true. When a proposition is made and accepted, then certain conclusions are implicit and explicit. So yes, I assume and conclude at the same time that God created the heavens and the earth in six normal days, and that He continues to sustain them to this very moment.
What is your basis for asserting differently about the origins and purpose of the universe? Do you even have any basis? Do you really believe you are operating without any assumptions or conclusions? If so, you've fooled yourself well, but you don't fool me.
I begin with a "conclusion," and I admit it. Is it a problem if I take your words at face value? Am I assuming a conclusion in so doing? Or must I subject all your statements to the rigors of scientific method before I accept them as true or false or somewhere in between?
And so, upon making this arbitrary decision that "it had to come from somewhere"
Such a decision is far from arbitrary. It would be arbitrary if I had a multiplicity of choices and then spun a spinner to make my choice. This one is about as basic and important as it gets. It is neither an arbitrary decision, nor it is one to be made arbitrarily, because it ultimately governs how I view the universe and interpret what it brings to my reason and senses. If you want to see the essence of "arbitrariness" at play in science, consider the semantic tap-dancing done in the name of "natural selection" and "random mutations;" the late and recent magic wands of evolutionary philosophers.
How do you know that intelligence is even required [to make a tree]?
I infer it from the fact that no other intelligent agent with which I am familiar admits to having the necessary tools and intelligence. What is it that prevents you from making a tree? Is it just a matter of the right mutations and natural selection occuring? What is it that prevents you from making a tree? What is there about a tree that you can design and implement without the aid of intelligence?