Fix "method_complexity" issue in src/main/java/io/github/clormor/hackerrank/advanced/visitor/TreeParser.java

[clormor]

Method processNode has a Cognitive Complexity of 7 (exceeds 5 allowed). Consider refactoring.

https://codeclimate.com/github/clormor/hacker-rank-java/src/main/java/io/github/clormor/hackerrank/advanced/visitor/TreeParser.java#issue_5d5373c621802a0001000042