This article presents a proposal of representation and scheme of exploratory visualization for Decision Trees in the KDD (Knowledge Discovery in Database) process, specifically in the data mining stage. With this, the improvement of the understandability of the internal operation of the model is pursued. This exploratory visualization is based on the well-known technique named Treemap (maps of trees) that allows representing hierarchical structures like the Decision Trees, being used grids to represent the nodes of the Decision Trees. The proposed visualization represents the number of instances or weight associated to a node with a scale of colors in degradation. In this way it is managed to heighten the rules of the Decision Trees in a 2D and 3D graphical representation of this visualization. Finally, a first attempt of subjective evaluation, based on for criteria, of the proposed visualization, is made. In this sense, this work pursues to introduce new schemes of visualizations that allow specifically understand how the data mining models work internally. (C) 2012 The Authors. Published by Elsevier Ltd.