What to do when the information gain on decision trees is 0 for all possible splits? I just started studying decisions trees and I am trying to construct a tree for a training set which uses Status as the class label. I am using the misclassification error as measure of impurity. After the first iteration, the information gain indicates that Department should be the tree root. The following table represents the sub-table for Department = Secretary. 



I got to this point and I don't know how to add the corresponding nodes to the tree. Should the next node be Age or Salary? 

Thanks!
You should process ALL of the possible splits and hope for information gain somewhere down the line.