A data tree is a unranked ordered tree where each position carries a label from a finite alphabet and a datum from some infinite domain. We consider the two variable first order logic {FO2(<,+1,~)} over data trees. Here {+1} refers to the child and the next sibling relations while {<} refers to the descendant and following sibling relations. Moreover {~} is a binary predicate testing data equality. We exhibit an automata model, denoted {DA#}, that is more expressive than {FO2(<,+1,~)} but such that emptiness of {DA#} and satisfiability of {FO2(<,+1,~)} are inter-reducible. This is proved via a model of counter tree automata, denoted {EBVASS}, that extends Branching Vector Addition Systems with States ({BVASS}) with extra features for merging counters. We show that, as decision problems, reachability for {EBVASS}, satisfiability of {FO2(<,+1,~)} and emptiness of {DA#} are equivalent.