Security risk treatment often requires a complex cost-benefit analysis to be carried out in order to select countermeasures that optimally reduce risks while having minimal costs. According to ISO/IEC 27001, risk treatment relies on catalogues of countermeasures, and the analysts are expected to estimate the residual risks. At the same time, recent advancements in attack tree theory provide elegant solutions to this optimization problem. In this paper we propose to bridge the gap between these two worlds by introducing optimal countermeasure selection problem on attack-defense trees into the TRICK security risk assessment methodology.