>I want to be able to see it not as huge big chunk of data, but normally with the tree structure (and have an ability to change something when looking at it this way).
>Also, files may be huge (~900KB or more)

If measurement scale or size is not a typo, search for the XML Notepad I mentioned.
Files > a few megabyte were checked -
workable, but not instantanuous on classic HD with CPU less capable than current.

Loads XML into a collapsed tree - of course has to parse file first.
Looking at
https://github.com/microsoft/XmlNotepad
there points to some maintainance done in 2020 and 2021,
Descriptive blurb on
https://microsoft.github.io/XmlNotepad/

Google also mentions Win10 as search option, even if any old XP program should run.
Probably safest thing to install on a company machine in MS-friendly surroundings
(if you do not employ VM under own control and IT security is doing their job)

HTH
thomas