public CollisionTreeNode(CollisionBox b,uint subdiv_level)
 {
     box = b;
     if (subdiv_level>0)
     {
         subdiv_level--;
         childs = new CollisionTreeNode[8];
         CollisionBox[] childs_box = box.GetChilds();
         for( uint i=0;i<8;i++ )
             childs[i] = new CollisionTreeNode(childs_box[i], subdiv_level);
     }
 }