For “std::vector<std::vector >” see [url=https://root-forum.cern.ch/t/storing-2d-vector-vector-vector-into-a-ttree/14331/2
For “std::vector<std::vectorstd::string >” see [url=https://root-forum.cern.ch/t/problem-in-getting-the-vector-vector-string-branch/14608/4
P.S. In the first above example, simply replace all occurrences of “float” with “int” and you’ll get “std::vector<std::vector >”.