Add examples of tree_of_thougts

[PengHongyiNTU]

Description

Add examples of tree_of_thougts, see examples/tree_of_thoughts/readme.md for more detail. All modifications are within the examples/tree_of_thoughts/

Checklist

Please check the following items before code is ready to be reviewed.

• [ ] Code has passed all tests
• [ ] Docstrings have been added/updated in Google Style
• [ ] Documentation has been updated
• [ ] Code is ready for review