I don't think we should have such a method at that service level: it mixes repository logic and  presentation problematic. What happen if we want a "--" in place of "└─" ?
I would really prefer to have a method like "def getActiveTechniqueByCategory(includeSystem:Boolean = false) : Box[SortedMap[List[ActiveTechniqueCategoryId], CategoryWithActiveTechniques]]" from ActiveTechniqueRepository (in 2.4.x), and an other for the display part (wich will be a trivial loop, since the size of the list give you both weither you want a "└─" and how many indentation are needed).