  For the tree topology, previous studies show the maximum likelihood estimate
(MLE) of a link/path takes a polynomial form with a degree that is one less
than the number of descendants connected to the link/path. Since then, the main
concern is focused on searching for methods to solve the high degree polynomial
without using iterative approximation. An explicit estimator based on the Law
of Large Numbers has been proposed to speed up the estimation. However, the
estimate obtained from the estimator is not a MLE. When $n<\infty$, the
estimate may be noticeable different from the MLE. To overcome this, an
explicit MLE estimator is presented in this paper and a comparison between the
MLE estimator and the explicit estimator proposed previously is presented to
unveil the insight of the MLE estimator and point out the pitfall of the
previous one.
