fix: print tree for subtrees

Author: kayjan

CHANGELOG.md

@@ -5,6 +5,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+### Fixed:
+- Tree Export: Print tree to display correctly for subtrees / non-root nodes.
 
 ## [1.0.0] - 2025-09-26
 ### Added:

bigtree/tree/export/_yield_tree.py

@@ -147,7 +147,7 @@ def yield_tree(self, strip: bool = True) -> Iterable[tuple[str, str, T]]:
         for _node in iterators.preorder_iter(self.tree):
             pre_str = ""
             fill_str = ""
-            if not _node.is_root:
+            if _node != self.tree:
                 node_depth = _node.depth - initial_depth
 
                 # Get fill_str (style_branch or style_stem_final)

tests/tree/export/test_stdout.py

@@ -82,6 +82,37 @@ def test_print_tree(tree_node):
             tree=tree_node,
         )
 
+    @staticmethod
+    def test_print_tree_subtree_b(tree_node):
+        # fmt: off
+        expected_str = (
+            "b\n"
+            "├── d\n"
+            "└── e\n"
+            "    ├── g\n"
+            "    └── h\n"
+        )
+        # fmt: on
+        assert_print_statement(
+            export.print_tree,
+            expected_str,
+            tree=tree_node["b"],
+        )
+
+    @staticmethod
+    def test_print_tree_subtree_c(tree_node):
+        # fmt: off
+        expected_str = (
+            "c\n"
+            "└── f\n"
+        )
+        # fmt: on
+        assert_print_statement(
+            export.print_tree,
+            expected_str,
+            tree=tree_node["c"],
+        )
+
     @staticmethod
     def test_print_tree_alias(tree_node):
         expected_str = (