Similar to (Tai et al., 2015), we opt for three stacked bi-LSTM, aiming at encoding individual phrases, sentences, and ultimately the whole essay in sequence.
according to the hierarchical structure from a parsing tree, the phrase-level bi-LSTM first encodes different phrases by consuming syntactic  Figure 2) from a lookup table of individual syntactic units in the tree; thereafter, the encoded dense layers in individual sentences are further consumed by a sentence-level bi-LSTM, ending up with sentence-level syntactic representations, which are ultimately combined by the essay-level bi-LSTM, resulting in − → e synt .