diff --git a/jedi/evaluate/base_context.py b/jedi/evaluate/base_context.py
index 37c86dba..c935826e 100644
--- a/jedi/evaluate/base_context.py
+++ b/jedi/evaluate/base_context.py
@@ -18,6 +18,8 @@ from jedi.evaluate.cache import evaluator_as_method_param_cache
 
 
 class HelperContextMixin:
+    tree_node = None
+
     @classmethod
     @evaluator_as_method_param_cache()
     def create_cached(cls, *args, **kwargs):
@@ -63,9 +65,7 @@ class Context(HelperContextMixin, BaseContext):
     """
     Should be defined, otherwise the API returns empty types.
     """
-
     predefined_names = {}
-    tree_node = None
     """
     To be defined by subclasses.
     """
diff --git a/jedi/evaluate/context/typing.py b/jedi/evaluate/context/typing.py
index 7366ed99..18ac383e 100644
--- a/jedi/evaluate/context/typing.py
+++ b/jedi/evaluate/context/typing.py
@@ -6,7 +6,8 @@ contexts.
 from jedi import debug
 from jedi.evaluate.cache import evaluator_method_cache
 from jedi.evaluate.compiled import builtin_from_name, CompiledObject
-from jedi.evaluate.base_context import ContextSet, NO_CONTEXTS, Context, iterator_to_context_set
+from jedi.evaluate.base_context import ContextSet, NO_CONTEXTS, Context, \
+    iterator_to_context_set, HelperContextMixin
 from jedi.evaluate.lazy_context import LazyKnownContexts, LazyKnownContext
 from jedi.evaluate.context.iterable import SequenceLiteralContext
 from jedi.evaluate.arguments import repack_with_argument_clinic, unpack_arglist
@@ -62,7 +63,7 @@ class _BaseTypingContext(Context):
 
     @property
     def name(self):
-        return ContextName(self, self.tree_name)
+        return ContextName(self, self._tree_name)
 
     def __repr__(self):
         return '%s(%s)' % (self.__class__.__name__, self._tree_name.value)
@@ -225,7 +226,7 @@ def _iter_over_arguments(maybe_tuple_context, defining_context):
         yield ContextSet.from_iterable(resolve_forward_references(context_set))
 
 
-class TypeAlias(object):
+class TypeAlias(HelperContextMixin):
     def __init__(self, evaluator, parent_context, origin_tree_name, actual):
         self.evaluator = evaluator
         self.parent_context = parent_context
diff --git a/jedi/evaluate/pep0484.py b/jedi/evaluate/pep0484.py
index f029e070..cac971c7 100644
--- a/jedi/evaluate/pep0484.py
+++ b/jedi/evaluate/pep0484.py
@@ -452,8 +452,6 @@ def find_annotation_variables(context, node):
             for subscript_node in _unpack_subscriptlist(trailer.children[1]):
                 type_var_set = context.eval_node(subscript_node)
                 for type_var in type_var_set:
-                    from jedi.evaluate.context.typing import TypeVar
-
                     if isinstance(type_var, TypeVar) and type_var not in found:
                         found.append(type_var)
     return found