My game freezes like that sometimes, too, though not with the Plantsim tree stump. It happens to my game when the processor/graphics driver have too much to do and they can't keep up with the demands of the game. To help, I lowered the graphics quality of the game and turned off some of the extra things, like reflective mirrors, etc. After that, my game worked fine.
So, my suggestion is, try lowering some/all of the settings, maybe?