add hierarchical node

include/links/LeafLink.h

@@ -5,5 +5,7 @@
 class LeafLink : public BaseLink {
 public:
 	using BaseLink::BaseLink;
-	void addChild(const NodePtr&) override { throw std::logic_error("LeafLink cannot have children"); }
+	void addChild(const NodePtr&) override {
+		throw std::logic_error("LeafLink cannot have children");
+	}
 };