We consider the problem of scheduling a tree with general communication delays. Jakoby and Reischuk proved that this problem is NP-hard for binary trees and unlimited number of processors. Firstly, we develop a clustering procedure based on the same lower bounds as Papadimitriou and Yannakakis for a related problem. We deduce an approximation algorithm for an unlimited number of processors with relative performance $2-1/(1+\rho)$, where $\rho$ denotes the maximum ratio between communication delays and duration of tasks. We also prove that, for a limited number of identical processors $m$, any list schedule using the clusters structure has a relative performance bounded by $1+(1-1/m)(2-1/(1+\rho))$ and that this bound is tight.