diff --git a/beetsplug/lastgenre/__init__.py b/beetsplug/lastgenre/__init__.py
index 72647f15c..388962b65 100644
--- a/beetsplug/lastgenre/__init__.py
+++ b/beetsplug/lastgenre/__init__.py
@@ -26,7 +26,7 @@ from __future__ import annotations
 
 from functools import singledispatchmethod
 from pathlib import Path
-from typing import TYPE_CHECKING, Any
+from typing import TYPE_CHECKING
 
 from beets import config, library, plugins, ui
 from beets.library import Album, Item
@@ -42,43 +42,6 @@ if TYPE_CHECKING:
     from beets.library import LibModel
 
 
-# Canonicalization tree processing.
-
-
-def flatten_tree(
-    elem: dict[Any, Any] | list[Any] | str,
-    path: list[str],
-    branches: list[list[str]],
-) -> None:
-    """Flatten nested lists/dictionaries into lists of strings
-    (branches).
-    """
-    if not path:
-        path = []
-
-    if isinstance(elem, dict):
-        for k, v in elem.items():
-            flatten_tree(v, [*path, k], branches)
-    elif isinstance(elem, list):
-        for sub in elem:
-            flatten_tree(sub, path, branches)
-    else:
-        branches.append([*path, str(elem)])
-
-
-def find_parents(candidate: str, branches: list[list[str]]) -> list[str]:
-    """Find parents genre of a given genre, ordered from the closest to
-    the further parent.
-    """
-    for branch in branches:
-        try:
-            idx = branch.index(candidate.lower())
-            return list(reversed(branch[: idx + 1]))
-        except ValueError:
-            continue
-    return [candidate]
-
-
 class LastGenrePlugin(plugins.BeetsPlugin):
     def __init__(self) -> None:
         super().__init__()
@@ -113,7 +76,7 @@ class LastGenrePlugin(plugins.BeetsPlugin):
         )
 
         loader = DataFileLoader.from_config(
-            self.config, self._log, Path(__file__).parent, flatten_tree
+            self.config, self._log, Path(__file__).parent
         )
         self.whitelist = loader.whitelist
         self.c14n_branches = loader.c14n_branches
@@ -133,7 +96,7 @@ class LastGenrePlugin(plugins.BeetsPlugin):
             return ("artist",)
         return tuple()
 
-    # More canonicalization and general helpers.
+    # Canonicalization and filtering.
 
     def _get_depth(self, tag: str) -> int | None:
         """Find the depth of a tag in the genres tree."""
@@ -153,6 +116,17 @@ class LastGenrePlugin(plugins.BeetsPlugin):
         depth_tag_pairs.sort(reverse=True)
         return [p[1] for p in depth_tag_pairs]
 
+    @staticmethod
+    def find_parents(candidate: str, branches: list[list[str]]) -> list[str]:
+        """Find parent genres of a given genre, ordered from closest to furthest."""
+        for branch in branches:
+            try:
+                idx = branch.index(candidate.lower())
+                return list(reversed(branch[: idx + 1]))
+            except ValueError:
+                continue
+        return [candidate]
+
     def _resolve_genres(self, tags: list[str]) -> list[str]:
         """Canonicalize, sort and filter a list of genres.
 
@@ -185,11 +159,11 @@ class LastGenrePlugin(plugins.BeetsPlugin):
                 if self.whitelist:
                     parents = [
                         x
-                        for x in find_parents(tag, self.c14n_branches)
+                        for x in self.find_parents(tag, self.c14n_branches)
                         if self._is_valid(x)
                     ]
                 else:
-                    parents = [find_parents(tag, self.c14n_branches)[-1]]
+                    parents = [self.find_parents(tag, self.c14n_branches)[-1]]
 
                 tags_all += parents
                 # Stop if we have enough tags already, unless we need to find
diff --git a/beetsplug/lastgenre/loaders.py b/beetsplug/lastgenre/loaders.py
index de71fb94d..3d650bd5e 100644
--- a/beetsplug/lastgenre/loaders.py
+++ b/beetsplug/lastgenre/loaders.py
@@ -56,7 +56,6 @@ class DataFileLoader:
         config: ConfigView,
         log: Logger,
         plugin_dir: Path,
-        flatten_func: Callable,
     ) -> DataFileLoader:
         """Create a DataFileLoader from plugin configuration.
 
@@ -77,7 +76,6 @@ class DataFileLoader:
             config["canonical"].get(),
             default_tree,
             config["prefer_specific"].get(),
-            flatten_func,
         )
 
         return cls(log, plugin_dir, whitelist, c14n_branches, canonicalize)
@@ -109,7 +107,6 @@ class DataFileLoader:
         config_value: str | bool | None,
         default_path: str,
         prefer_specific: bool,
-        flatten_func: Callable,
     ) -> tuple[list[list[str]], bool]:
         """Load the canonicalization tree from a YAML file.
 
@@ -129,5 +126,24 @@ class DataFileLoader:
             log.debug("Loading canonicalization tree {}", c14n_filename)
             with Path(c14n_filename).expanduser().open(encoding="utf-8") as f:
                 genres_tree = yaml.safe_load(f)
-            flatten_func(genres_tree, [], c14n_branches)
+            DataFileLoader.flatten_tree(genres_tree, [], c14n_branches)
         return c14n_branches, canonicalize
+
+    @staticmethod
+    def flatten_tree(
+        elem: dict | list | str,
+        path: list[str],
+        branches: list[list[str]],
+    ) -> None:
+        """Flatten nested lists/dictionaries into lists of strings (branches)."""
+        if not path:
+            path = []
+
+        if isinstance(elem, dict):
+            for k, v in elem.items():
+                DataFileLoader.flatten_tree(v, [*path, k], branches)
+        elif isinstance(elem, list):
+            for sub in elem:
+                DataFileLoader.flatten_tree(sub, path, branches)
+        else:
+            branches.append([*path, str(elem)])