Added the cycle detection functionality to the Tree class.
Made better comments for new alterations to the Tree class
Added reset method to the setDepth method.
Made a tests for the Tree class functionalities.
Made minor corrections after feedback on pull request.
Made better test. The ones before, although correct, were poorly written and not flexible at all.
Used autopep8 for PEP8 conventions.
PEP8 conventions to the test file.
Merge pull request #175 from petermlm/develop

Cycle detection in the Tree calss