Update tree_helper.rb to fix #31784, which broken file browse where paths deeper than 6:'/'.

What does this MR do?

fix issue #31784 (closed), which broke file tree browse after commit df36f1f4.

Are there points in the code the reviewer needs to double check?

no.

Why was this MR needed?

fix critical bug.

Screenshots

no.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #31784 (closed)