Fix converting list of paths to nested dicts

src/cal_tools/h5_copy_except.py

@@ -2,9 +2,10 @@ import h5py
 
 def paths_to_tree(paths):
     """Convert paths to a nested-dict tree, with True at leaves"""
-    tree = tree_part = {}
+    tree = {}
     
     for path in paths:
+        tree_part = tree
         path_names = path.strip('/').split('/')
         for name in path_names[:-1]:
             tree_part = tree_part.setdefault(name, {})