In this paper, we investigate unit refutability in Unit Two Variable Per Inequality (UTVPI) Constraint Systems (UCSs). A Unit Two Variable Per Inequality (UTVPI) constraint is a linear relationship of the form: \(\pm x_{i}\pm x_{j} \le b_{ij}\) , where \(b_{ij} \in \mathbb {Z}\) . A UCS is a conjunction of such constraints. If it is required that the two variables in a UTVPI constraint have opposite signs, then the constraint is called a difference constraint and a conjunction of such constraints is called a difference constraint system (DCS). When a decision procedure deems a UCS is infeasible, it is important to provide a certificate which attests to the infeasibility of the UCS. Such a certificate is called a negative certificate. Refutations (under an appropriate refutation system) form an important subclass of negative certificates. All problems in the complexity class P have succinct negative certificates. We focus on a subclass of refutations called Unit Refutations (UR). The UR refutation system is incomplete, in that unsatisfiable UCSs may not have unit refutations. However, they are useful from the perspective of identifying variable domains responsible for system inconsistency. Previous work has examined dag-like unit refutations of UCSs [18]. In this paper, we examine tree-like unit refutations of UCSs.