code: def tree_iter_nexson_proxy(nexson_proxy):
      
      nexml_el = nexson_proxy._nexml_el
      tg_order = nexml_el['^ot:treesElementOrder']
      tgd = nexml_el['treesById']
      for tg_id in tg_order:
          tg = tgd[tg_id]
          tree_order = tg['^ot:treeElementOrder']
          tbid = tg['treeById']
          otus = tg['@otus']
          for k in tree_order:
              v = tbid[k]
              yield nexson_proxy._create_tree_proxy(tree_id=k, tree=v, otus=otus)
docs: Iterates over NexsonTreeProxy objects in order determined by the nexson blob