Creates new entry for UI/UX Tree Testing

[flavianoneto]

Description

This PR adds a new concept entry titled Tree Testing to the Codecademy Docs under the UI/UX category. The file tree-testing.md was created in the tree-testing directory. The entry provides an overview of tree testing as a usability testing method, its applications in UI/UX design, tools for conducting tree testing, and additional resources for further learning.

The motivation for this addition is to expand the Codecademy Docs' coverage of UI/UX concepts, providing learners with a comprehensive understanding of tree testing and its role in improving information architecture.

Issue Solved

Closes #6561

Type of Change

• Adding a new entry

Checklist

• All writings are my own.
• My entry follows the Codecademy Docs style guide.
• My changes generate no new warnings.
• I have performed a self-review of my own writing and code.
• I have checked my entry and corrected any misspellings.
• I have made corresponding changes to the documentation if needed.
• I have confirmed my changes are not being pushed from my forked main branch.
• I have confirmed that I'm pushing from a new branch named after the changes I'm making.
• I have linked any issues that are relevant to this PR in the Issues Solved section.

[CLAassistant]

All committers have signed the CLA.

[dakshdeepHERE]

I'm closing this PR as the issue was already claimed by some other author @flavianoneto, please claim some other issue.