refactor(tree): clean code

[aniaan]

1. make the node of ntParam have the correct prefix
2. clean up the code and make it more readable

[pkieltyka]

thanks for the PR -- for (1) does this fix any particular issues / cases you've identified?

[aniaan]

thanks for the PR -- for (1) does this fix any particular issues / cases you've identified?

No, only the node related to ntRegexp uses the prefix field during the whole run, the node of ntParam does not use the prefix field, so whether the ntParam node has the correct prefix field or not does not affect the correctness of the program.
But in terms of the positioning of the prefix field, having the ntParam node have the correct prefix field will help to understand the code better.

The above issues are all some nuisances in reading the code, and if fixed, the readability of the code would be a little better.