(1) Remove leaf nodes which are not link nodes; (2) If the node is the only child of of its parent node, delete the parent node and directly connect the node with its ancestor node; (3) If the node has two children nodes, and the first child node is the link node, while the other is not, then delete the node and connect the two children nodes with its ancestor node.
classification and clustering: Expected cross Entropy is selected for feature selection.