src/Baum/Node.php
public function getLeftSibling() {
    return $this->siblings()
                ->where($this->getLeftColumnName(), '<', $this->getLeft())
                ->orderBy($this->getOrderColumnName(), 'desc')
                ->get()
                ->last();
  }
public function getLeftSibling() {
    return $this->siblings()
                ->where($this->getLeftColumnName(), '<', $this->getLeft())
                ->orderBy($this->getOrderColumnName(), 'desc')
                ->get()
                ->last();
  }
Returns the first sibling to the left.

@return NestedSet