Hierarchical structures of the clusters in NGC 6334. (a) The background is the surface density of stars. The black and orange contours show the masks of leaf and branch clusters, respectively. The magenta, red, and cyan cycles are the approximated ellipses with effective radii R_eff, R_eff, 1, and R_eff, 2 defined in Sect. 3.3, respectively. (b) The dendrogram tree shows the hierarchical cluster structures.