defining a function to set up the branches in a concise way
Currently, setting up a branch requires at least two lines, e.g.
Type * var = nullptr;
tree->SetBranchAddress("branch", &var);
This gets longer in case we want to take advantage of the TTree
friendship. In this MR, a function is introduced to set up branches in a single line. In addition, this function may throw an exception in case the branch is not found.