code: def tree_field(v):
      def post(ls):
          batch = len(ls)
          lengths = [l[-1][1] for l in ls]
          length = max(lengths) + 1
          ret = torch.zeros(batch, length, length, 10 + len(v.vocab))
          for b in range(len(ls)):
              for i, j, n in ls[b]:
                  if i == j:
                      ret[b, i, j, v.vocab.stoi[n] + 1] = 1
                  else:
                      ret[b, i, j, 0] = 1
          return ret.long()
  
      return post
  
file_path: pytorch-struct/examples/data/trees.py
imports: import torchtext.data
  import torch
label_desc: Use image node_id 1 for calling the ListOpsDataset obj's underlying member method code with example usage: obj.tree_field(v) and returns: post, ret