Also interviewing with other companies. The next best job for you may not be with Google even if you could easily get an internal transfer role. And teams don't just blindly accept you because you already work at Google (although it helps). You still have to go through a somewhat more informal interview loop that you will definitely want to prepare for.
Of course this is up to the individual, you can definitely just screw around for awhile and apply for an interal role with much less care.
I've dealt with trees in every single domain I've been in, frontend or backend, whether doing "real" programming or building with no-code tools like FileMaker. I've seen admins and accountants build trees and recursion with spreadsheets. I don't think these things are as "gatekeeping" as you imagine.
I don't agree that all jobs have to deal with trees either.
There are other teams where there is little need for more formal process.
I think 3-4 moved within the company, 3 left on their own time before the deadline, and 4 waited out for the redundancy payment.