Kara walks the slalom in an endless loop around the trees. He alternates left and right turns as follows:

while (true) {
  while (kara.treeLeft() && !kara.treeRight()) {
    quarterTurnLeft();
  }
  quarterTurnRight();
  while (!kara.treeLeft() && kara.treeRight()) {
    quarterTurnRight();
  }
  quarterTurnLeft();
}