diff --git a/libwyag.py b/libwyag.py
index de56aa3..7dde8f8 100644
--- a/libwyag.py
+++ b/libwyag.py
@@ -581,13 +581,14 @@ def ls_tree(repo, ref, recursive=None, prefix=""):
             type = item.mode[0:2]
 
         match type:
-            case b'04': type = "tree"
+            case b'04': raise Exception("Trees should point to subcommits, not other trees")
             case b'10': type = "blob"
             case b'12': type = "blob" # a symlink
             case b'16': type = "commit" # a submodule
+            case b'sc': type = "subcommit"
             case _: raise Exception(f"Weird tree leaf mode {item.mode}")
 
-        if not (recursive and type=='tree'): # This is a leaf
+        if not (recursive and type=='subcommit'): # This is a leaf
             print("{0} {1} {2}\t{3}".format(
                 "0" * (6 - len(item.mode)) + item.mode.decode("ascii"),
                 # Git's ls-tree displays the type
@@ -596,8 +597,11 @@ def ls_tree(repo, ref, recursive=None, prefix=""):
                 item.sha,
                 join_path(prefix, item.path)
             ))
-        else: # This is a branch (vs. leaf), recurse
-            ls_tree(repo, item.sha, recursive, join_path(prefix, item.path))
+        else: # This is a subcommit
+            commit_obj = object_read(repo, item.sha)
+            tree_sha = commit_obj.kvlm[b'tree'].decode("ascii")
+            ls_tree(repo, tree_sha, recursive, join_path(prefix, item.path))
+
 
 argsp = argsubparsers.add_parser("checkout", help="Checkout a commit inside of a directory.")
 
@@ -1112,13 +1116,19 @@ def tree_to_dict(repo, ref, prefix=""):
         # We read the object to extract its type (this is uselessly
         # expensive: we could just open it as a file and read the
         # first few bytes)
-        is_subtree = leaf.mode.startswith(b'04')
+        if (leaf.mode.startswith(b'04')):
+            raise Exception("Tree should not be child of tree")
+
+        is_subcommit = leaf.mode.startswitch(b'sc')
 
         # Depending on the type, we either store the path (if it's a
         # blob, so a regular file), or recurse (if it's another tree,
         # so a subdir)
-        if is_subtree:
-            ret.update(tree_to_dict(repo, leaf.sha, full_path))
+        if is_subcommit:
+            commit_obj = object_read(repo, leaf.sha)
+            tree_sha = commit_obj.kvlm[b'tree'].decode("ascii")
+
+            ret.update(tree_to_dict(repo, tree_sha, full_path))
         else:
             ret[full_path] = leaf.sha
 
@@ -1367,7 +1377,42 @@ def gitconfig_user_get(config):
             return f"{config['user']['name']} <{config['user']['email']}>"
     return None
 
-def tree_from_index(repo, index):
+def create_commit_map(repo, commit):
+    commit_map = dict()
+
+    create_commit_map_recurse(repo, commit, commit_map, "")
+
+    return commit_map
+
+def create_commit_map_recurse(repo, commit, commit_map, path):
+    """From a root commit, walk down the tree of subcommits. Returns a dict mapping
+    directory paths to commit objects. Note: doesn't include root commit."""
+
+    tree_sha = commit.kvlm["tree"].decode('ascii')
+    obj = object_read(repo, tree_sha)
+    for item in obj.items:
+        if len(item.mode) == 5:
+            type = item.mode[0:1]
+        else:
+            type = item.mode[0:2]
+
+        match type:
+            case b'04': raise Exception("Trees should point to subcommits, not other trees")
+            case b'10': type = "blob"
+            case b'12': type = "blob" # a symlink
+            case b'16': type = "commit" # a submodule
+            case b'sc': type = "subcommit"
+            case _: raise Exception(f"Weird tree leaf mode {item.mode}")
+
+        if type == "subcommit":
+            fullpath = f"{path}/{item.path}"
+            subcommit = object_read(repo, item.sha)
+            commit_map[fullpath] = subcommit
+
+            create_commit_map_recurse(repo, subcommit, commit_map, fullpath)
+
+
+def tree_from_index(repo, index, commit_map, author, commit_time, message):
     contents = dict()
     contents[""] = list()
 
@@ -1411,6 +1456,15 @@ def tree_from_index(repo, index):
 
         sha = object_write(tree, repo)
 
+        subcommit = commit_map[path]
+
+        new_subcommit = commit_create(repo,
+                                      sha,
+                                      subcommit,
+                                      author,
+                                      commit_time,
+                                      message)
+
         parent = os.path.dirname(path).replace("\\", "/")
         base = os.path.basename(path)
         contents[parent].append((base, sha))
@@ -1441,13 +1495,25 @@ def commit_create(repo, tree, parent, author, timestamp, message):
 def cmd_commit(args):
     repo = repo_find()
     index = index_read(repo)
-    tree = tree_from_index(repo, index)
+    root_commit = object_find(repo, "HEAD")
+
+    commit_time = datetime.now()
+    author = gitconfig_user_get(gitconfig_read())
+
+    commit_map = create_commit_map(repo, root_commit)
+
+    tree = tree_from_index(repo,
+                           index,
+                           commit_map,
+                           author,
+                           commit_time,
+                           args.message)
 
     commit = commit_create(repo,
                            tree,
-                           object_find(repo, "HEAD"),
-                           gitconfig_user_get(gitconfig_read()),
-                           datetime.now(),
+                           root_commit,
+                           author,
+                           commit_time,
                            args.message)
 
     # Update HEAD so our commit is now the tip of the active branch.