build_tree
build_tree(s, (tree_desc *)(&(s->l_desc)));
build_tree(s, (tree_desc *)(&(s->d_desc)));
build_tree(s, (tree_desc *)(&(s->bl_desc)));
build_tree(s, (tree_desc *)(&(s->l_desc)));
build_tree(s, (tree_desc *)(&(s->d_desc)));
build_tree(s, (tree_desc *)(&(s->bl_desc)));