In M. Lucido et al. (2004) and M. Lucido et al. (2006) a new approach has been introduced, based on the method of analytical regularization (MAR):: it is shown that the use of a Galerkin scheme with expansion functions ensuring the correct edge behaviour and continuity conditions of the current allows for an efficient solution of the electric and magnetic field integral equations (EFIE and MFIE) describing the problem, achieving a quick convergence, and therefore small matrices to be numerically computed, and an effective control of the truncation error, which is quite difficult by using other conventional numerical methods. In M. Lucido et al. (2006) the method has been extended to the analysis of open polygonal cylinders, for which the MFIE cannot be used. A further generalization is presented in the present contribution, in order to analyze a "tree-shaped" open structure, which is useful, for instance, in radio propagation modeling.