diff --git a/pkg/repository/comment.go b/pkg/repository/comment.go
index 3789b4b..a54101d 100644
--- a/pkg/repository/comment.go
+++ b/pkg/repository/comment.go
@@ -110,7 +110,12 @@ func (repo *CommentRepository) ListComments(ctx context.Context, req repository.
 	filter := bson.M{}
 	if req.ParentID != nil {
 		filter["parent_comment_id"] = req.ParentID
+	} else {
+		filter["parent_comment_id"] = bson.M{
+			"$in": []interface{}{"", nil},
+		}
 	}
+
 	if req.ReferenceID != nil {
 		filter["reference_id"] = req.ReferenceID
 	}