diff --git a/stanza/models/constituency/parser_training.py b/stanza/models/constituency/parser_training.py
index 0711f5aea..bddc40e07 100644
--- a/stanza/models/constituency/parser_training.py
+++ b/stanza/models/constituency/parser_training.py
@@ -620,22 +620,27 @@ def contrast_trees(reparsed, gold):
                 if reparsed.is_preterminal() or gold.is_preterminal():
                     return
 
-                if (len(reparsed.children) == len(gold.children) and
-                    all(x.start_index == y.start_index and x.end_index == y.end_index for x, y in zip(reparsed.children, gold.children))):
-                    for x, y in zip(reparsed.children, gold.children):
-                        contrast_trees(x, y)
-                    return
-
-                # TODO: instead compare all subtrees?
-                # preterminals don't have values returned by the tree analysis functions above
-                if (reparsed.children[0].end_index != gold.children[0].end_index and
-                    not reparsed.children[0].is_preterminal() and not gold.children[0].is_preterminal()):
-                    reparsed_negatives.append(reparsed_hx[str(reparsed.children[0])])
-                    gold_negatives.append(gold_hx[str(gold.children[0])])
-                if (reparsed.children[-1].start_index != gold.children[-1].start_index and
-                    not reparsed.children[-1].is_preterminal() and not gold.children[-1].is_preterminal()):
-                    reparsed_negatives.append(reparsed_hx[str(reparsed.children[-1])])
-                    gold_negatives.append(gold_hx[str(gold.children[-1])])
+                reparsed_idx = 0
+                gold_idx = 0
+                while reparsed_idx < len(reparsed.children) and gold_idx < len(gold.children):
+                    reparsed_child = reparsed.children[reparsed_idx]
+                    gold_child = gold.children[gold_idx]
+                    if not reparsed_child.is_preterminal() and not gold_child.is_preterminal():
+                        # TODO: check that comparing labels is helpful
+                        if (reparsed_child.label == gold_child.label and
+                            reparsed_child.start_index == gold_child.start_index and
+                            reparsed_child.end_index == gold_child.end_index):
+                            contrast_trees(reparsed_child, gold_child)
+                        else:
+                            reparsed_negatives.append(reparsed_hx[str(reparsed_child)])
+                            gold_negatives.append(gold_hx[str(gold_child)])
+                    if reparsed_child.end_index == gold_child.end_index:
+                        reparsed_idx += 1
+                        gold_idx += 1
+                    elif reparsed_child.end_index < gold_child.end_index:
+                        reparsed_idx += 1
+                    else:
+                        gold_idx += 1
 
             reparsed_tree.mark_spans()
             gold_tree.mark_spans()