Tree structures have gained popularity for storing data from different domains such as XML documents, bio informatics and so on. Clustering these data can facilitate different operations. In this paper, we propose TreeCluster, a novel and heuristic algorithm for clustering tree structured data. This algorithm considers a representative tree for each cluster. For each input tree T, TreeCluster computes the composition of the tree T and each of the clusters. Tree T belongs to the cluster which its composed tree gains the best score. After adding a tree to a cluster the representative tree of that cluster is updated. We evaluate the accuracy of the TreeCluster algorithm in comparison to the previous works