Fixed return type
Merged with upstream
Added tests for functions 4-11
Modified functions 12-23
Added more tests
Reviewed functions 25-30
Merge remote-tracking branch 'upstream/master'

Merge any changes made upstream.
Worked on functions 30-35
Merge remote-tracking branch 'upstream/master'

Merging tree.py
Finished revisions for functions 8-18
Finished tests for functions 0-18
Merge remote branch 'upstream/master'