Decision tree computation complexity

The computational complexity of the algorithm given training set D is O(n*|D| log(|D|)), where n is the number of attributes describing the tuples in D and |D| is the number of training tuples in D. This means that the computational cost of growing a tree grows at most n Dlog(|D|) with |D| tuples.I am not able to log(|D|)part specifically. Refrenece-Book Data minning concepts and tech.2nd edition page number 296 topic-Classification and prediction(Chapter 6)