决策树模型的流程梳理

https://nbviewer.jupyter.org/github/donggu26/donggu/blob/master/%E5%86%B3%E7%AD%96%E6%A0%91%E6%A8%A1%E5%9E%8B%E7%9A%84%E4%B8%80%E4%BA%9B%E6%93%8D%E4%BD%9C.ipynb