Algorithm 2 Pruning algorithm

1. Calculate the information gain of each node. 2. Recursively upwardly from the leaf node of the tree, calculate the loss of the leaf node before and after the parent node: $C_{\alpha }\left(TB\right)$ and $C_{\alpha }\left(TA\right)$. If $C_{\alpha }\left(TA\right)<C_{\alpha }\left(TB\right)$: Prune. 3. Repeat step 2 until it cannot continue.