Tree-based group key agreement protocol that allows group members to compute the group key based on their individual contributions can provide verifiable trust relationship between participants in ad-hoc networks. We discuss the principles and structural features of three tree-based group key agreement protocols, and compare the communication and computation that generated by each protocol when their members are adding, leaving, merging or breaking up. The analysis and comparison results show that each tree-based group key agreement protocol is applicable to corresponding ad-hoc network. We also provide reference and technical support for application of more complicated tree structure in ad-hoc networks.