fixed the tree print issue

[GuiLingfeng]

PR Summary:

fixed the issue not being able to print the hireachy. related to the issue (https://github.com/mosdef-hub/mbuild/issues/1143)

PR Checklist

---

• [ ] Includes appropriate unit test(s)
• [ ] Appropriate docstring(s) are added/updated
• [ ] Code is (approximately) PEP8 compliant
• [ ] Issue(s) raised/addressed?

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (9499a8c) 87.18% compared to head (3f1182b) 87.18%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #1155 +/- ## ======================================= Coverage 87.18% 87.18% ======================================= Files 62 62 Lines 6492 6492 ======================================= Hits 5660 5660 Misses 832 832 ```

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