title: How to get the MSE of the node in the DecisionTreeRegressor of scikit-learn?
body: <p>In the generated decision tree regression model, there is an MSE attribute when using <code>graphviz</code> to view the tree structure. I need to obtain the MSE of each leaf node, and carry out subsequent operations according to the MSE. However, after reading the document, I can't find the method to provide for output MSE. Other attributes such as feature name, sample number, prediction value, etc. All have are corresponding methods:</p>
  
  <p><a href="https://i.stack.imgur.com/Vfwrg.png" rel="noreferrer"><img src="https://i.stack.imgur.com/Vfwrg.png" alt="Tree structure"></a></p>
  
  <p>With <code>help(sklearn.tree._tree.Tree)</code>, I can see that most of the attributes have some methods to output the value, but I don't see anything about MSE.</p>
  
  <p>Help on class Tree in module sklearn.tree._tree
  <a href="https://i.stack.imgur.com/33Bf5.png" rel="noreferrer"><img src="https://i.stack.imgur.com/33Bf5.png" alt="Help on class Tree in module sklearn.tree._tree"></a></p>