For a fair comparison with the sequential model, we apply the same formulation of LSTM on the binarized constituent parse tree. The hidden state vector now corresponds to a constituent in the tree. These hidden state vectors are then used in the same fashion as the sequential LSTM. The mathematical formulation is the same as Tai et al. (2015) . This model is similar to the recursive neural networks proposed by<cite> Ji and Eisenstein (2015)</cite> .