diff --git a/src/laptrack/data_conversion.py b/src/laptrack/data_conversion.py
index 0dabdca7..c08a352d 100644
--- a/src/laptrack/data_conversion.py
+++ b/src/laptrack/data_conversion.py
@@ -5,8 +5,11 @@
 import numpy as np
 import pandas as pd
 
+from ._typing_utils import Int
 from ._typing_utils import NumArray
 
+IntTuple = Tuple[Int, Int]
+
 
 def convert_dataframe_to_coords(
     df: pd.DataFrame,
@@ -88,8 +91,8 @@ def convert_tree_to_dataframe(
     #            tree.nodes[(frame, index)]["tree_id"] = track_id
     tree2 = tree.copy()
 
-    splits = []
-    merges = []
+    splits: List[Tuple[IntTuple, List[IntTuple]]] = []
+    merges: List[Tuple[IntTuple, List[IntTuple]]] = []
     for node in tree.nodes:
         frame0, _index0 = node
         neighbors = list(tree.neighbors(node))
@@ -101,13 +104,13 @@ def convert_tree_to_dataframe(
                 if tree2.has_edge(node, child):
                     tree2.remove_edge(node, child)
             if node not in [p[0] for p in splits]:
-                splits.append([node, children])
+                splits.append((node, children))
         if len(parents) > 1:
             for parent in parents:
                 if tree2.has_edge(node, parent):
                     tree2.remove_edge(node, parent)
             if node not in [p[0] for p in merges]:
-                merges.append([node, parents])
+                merges.append((node, parents))
 
     connected_components = list(nx.connected_components(tree2))
     for track_id, nodes in enumerate(connected_components):