trecurse
trecurse(vroot, action, 0);
trecurse(root->llink, action, level + 1);
trecurse(root->rlink, action, level + 1);
trecurse(root->llink, action, level + 1);
trecurse(root->rlink, action, level + 1);
trecurse(vroot, action, 0);