Different with standard RNN, there are no nonterminal nodes in dependency tree.
each node h in dependency tree has two associated distributed representations: 1. word embedding w h ∈ R m , which is denoted as its own information according to its word form; 2. phrase representation x h ∈ R m , which is denoted as the joint representation of the whole subtree rooted at h. when h is leaf node, Given a subtree rooted at h in dependency tree, we define c i , 0 < i ≤ L as the i-th child node of h, where L represents the number of children.