Draw Trees with netwokx

https://stackoverflow.com/questions/11479624/is-there-a-way-to-guarantee-hierarchical-output-from-networkx

(note for Anaconda)
https://stackoverflow.com/questions/13987353/python-valueerror-program-dot-not-found-in-path

sudo apt-get install python-dev

sudo apt-get install graphviz-dev

sudo apt-get install graphviz

pip3 install pygraphviz