An information processing device according to an embodiment includes one or more processors. The processors perform hierarchical clustering of a key phrase group. The processors divide the key phrase group into candidate clusters. The processors receive a selectin operation of one item from predetermined items for classifying the document group. The processors calculate, for each candidate cluster, a score indicating utility with respect to the selected item. The processors decide, as a reference cluster, a candidate cluster for which the score has a predetermined ranking. The processors divide the reference cluster into sub-clusters. The processors extract predetermined sub-items in the lower levels of the selected item. And the processors control presentation of an expansion image for expressing the information volume of the documents for each sub-item and each sub-cluster.