public static extern int nk_tree_state_image_push( nk_context *ctx, nk_tree_type tree_type, nk_image img, byte *title, nk_collapse_states *state );
public static extern int nk_tree_push_hashed( nk_context *ctx, nk_tree_type tree_type, byte *title, nk_collapse_states initial_state, byte *hash, int len, int seed );