See also the following links:

▎ENGLISH

Decision Tree Algorithm Explained!
▸ https://medium.com/analytics-vidhya/decision-tree-algorithm-explained-bd6b7b22eab9

Decision Trees: Gini vs Entropy
▸ https://quantdare.com/decision-trees-gini-vs-entropy/

▎日 本 語

決定木分析（ディシジョンツリー）とは？概要や活用方法
▸ https://cacoo.com/ja/blog/what-is-decision-tree/

[決定木]ジニ不純度と戯れる
▸ https://qiita.com/murs313/items/0a2077f97664b58c2ea9

初心者の初心者による初心者のための決定木分析
▸ https://qiita.com/3000manJPY/items/ef7495960f472ec14377