Include a method that will print the depth-first traversal of a tree (choosing left branches first). public void printDepthFirst() { ... } For example, for the tree

                                              t =                     3
                                                                   /          \
                                                                  /             \
                                                                 4               5
                                                             /        \       /        \
                                                             6         7      8        9

the call t.printDepthFirst(); should print 3 4 6 7 5 8 9