There is no safe quadrocopter now. You got to plan missions in UGCS with 3D ground level, only this thing will help to you with known obstacles. UGCS is only for flying above forest.
You can’t fly inside the forest. Better use some special photo mast.
But if you want to try - you can use UGCS No fly zone:
Or DroneHarmony for Android, it have advanced noflyzone editing. But I’m shure it’s bad idea to fly in forest)