3D Oaktree model

Hi I need 3D Oak tree model for my unity project. It needs to be in 3 detalisations: A - So that about 500 of those trees can bee seen in one mobile screen B - Something more detailed C - Full detail oak tree, but it must be possible to see it on most modern phones without lagging. For that full detail tree i need some animation, it can be acorns falling from time to time.. it can be some squirrel running around sometimes.. or just leafs weaving in light wind (i just dont know how hard it is to do those animations) It will be used in application for mobiles.. where you look through camera at some box with markers and there is virtual tree growing, and you can go around it and look little bit closer. Those animation (squirrel) must be in size, so it can be seen. It must be in format that can be imported into Unity. Maybe someone of you already have some nice Oak tree.. I attached some pictures with oak trees i like. Thank you