Kara walks around the trees in an endless loop. In each step, he considers the sensors "tree front?" and "tree right?" to determine the appropriate action.

while (true) {
  if (kara.treeFront() && kara.treeRight()) {
    kara.turnLeft();
  }
  else if (!kara.treeFront()) {
    if (kara.treeRight()) {
      kara.move();
    }
    else {
      kara.turnRight();
      kara.move();
    }
  }
}