Note: Since adjacent dialects may co-evolve for centuries, a discrete tree model is often inappropriate. There are three ways to form 2/1 clades of a 3-way branching like Common Germanic and all three (North+West = Northwest, North+East = Northeast and West+East = South) have been proposed!
Note: Germanic is shown with two parents because it is a hybrid of two northern I-E dialects, one each from Centum and Satem groups. Such hybrids may be unusual, but can arise when the two dialects are mutually intelligible (or nearly so). (Germanic is something of a mystery for I-E specialists; the conclusion that it is a hybrid results from recent work by Prof. Ringe.)