ns_tree_node_add
struct rb_node *ns_tree_node_add(struct ns_tree_node *node,
node = ns_tree_node_add(&ns->ns_tree_node, ns_tree, ns_cmp);
ns_tree_node_add(&ns->ns_unified_node, &ns_unified_root, ns_cmp_unified);
ns_tree_node_add(&ns->ns_owner_node, &owner->ns_owner_root, ns_cmp_owner);