/in/ex6.cpp:29:43: error: extra ';' [-Werror=pedantic]
 BinaryTree::BinaryTree() : root(nullptr){};
                                           ^
/in/ex6.cpp: In function 'std::ostream& operator<<(std::ostream&, const BinaryTree&)':
/in/ex6.cpp:102:52: error: unused parameter 'tree' [-Werror=unused-parameter]
 ostream &operator<<(ostream &os, const BinaryTree &tree)
                                                    ^~~~
cc1plus: all warnings being treated as errors
/in/compile/Makefile:69: recipe for target 'ex6.o' failed
make: *** [ex6.o] Error 1