script.on_nth_tick(60, 
    function(event)
        -- event has fields: tick, nth_tick

        -- At 10 seconds, create a biter, some trees, and command the biter to attack the trees
        if event.tick == 10 * 60 then
            local surface = game.surfaces["nauvis"]
            global.biter = surface.create_entity({name = "small-biter", position = {x = 5.0, y = 0.0}, force = game.forces["player"]})

            -- Create some trees
            global.trees = {}
            for i = 1,3 do
                global.trees[i] = surface.create_entity({name = "tree-04", position = {x = 10.0 + i, y = 0.0}, force = game.forces["neutral"]})
            end

            -- Create unit group
            global.unit_group = surface.create_unit_group({position = {x = 5.0, y = 0.0}, force = game.forces["player"]})
            global.unit_group.add_member(global.biter)

            -- Attack the trees
            local commands = {}
            for _, e in ipairs(global.trees) do
                e.order_deconstruction(game.forces["player"])
                commands[#commands + 1] = {type = defines.command.attack, target = e}
            end

            global.unit_group.set_command({type = defines.command.compound, structure_type = defines.compound_command.logical_and, commands = commands})
            game.print("Created biter and trees")

        -- At 11 seconds, destroy a tree before the biter gets to it
        elseif event.tick == 11 * 60 then
            if global.trees[2].valid then
                global.trees[2].destroy({})
                game.print("Second tree destroyed")
            end
        end
    end
)