Collatz Trees:<em> </em>Trunk–Branch Indexing and Affine Cycle-Freeness

The Collatz Conjecture remains one of the most enduring unsolved problems in mathematics, despite being based on an extraordinarily simple rule. Given any natural number \( n \), the conjecture posits that repeatedly applying the operation—dividing by 2 if even, or multiplying by 3 and adding 1 if odd—will eventually result in the number 1. This paper develops a structural perspective by proposing the Collatz Tree as a framework to organize and visualize natural numbers. Each branch is the geometric ray \( \{k\cdot 2^b\}_{b\ge 0} \) for an odd odd core \( k \), and the trunk is the ray from 1. We introduce a trunk—branch indexing that bijects \( N \) with \( Z_{\ge 0}×Z_{\ge 0} \). Algebraically, we encode Collatz steps as affine maps and prove absence of nontrivial finite cycles for a three-way map \( T \); via a bridge, this implies the same for the standard accelerated map \( A(n)=(3n+1)/2^{v2(3n+1)} \) on odd integers. Thus the global Collatz convergence reduces to an independent pillar: coverage (reachability) of the inverse tree rooted at 1, isolating cycle-freeness from coverage and reducing the conjecture to the remaining reachability pillar. Prior work (e.g., Kosobutskyy) studied reverse-oriented trees via Jacobsthal sequences, emphasizing periodic and statistical aspects. Our approach differs in both formulation and aim: we build a tree rooted at 1 and give a constructive, graph-theoretic route toward cycle-freeness and reduction to coverage.