See also the following links:

▎ENGLISH

How to Get Started With Regression Trees
▸ https://builtin.com/data-science/regression-tree

Regression Trees in R
▸ https://uc-r.github.io/regression_trees

▎日 本 語

回帰の決定木アルゴリズムを完全図解する
▸ https://datawokagaku.com/decision_tree/

決定木による回帰
▸ http://taustation.com/decision-tree-regression/