Split graph folder into graph and tree

tree/directed_rooted_tree.h

@@ -0,0 +1,20 @@
+#ifndef DIRECTED_ROOTED_TREE_H_
+#define DIRECTED_ROOTED_TREE_H_
+
+#include "tree.h"
+using namespace graph;
+
+namespace tree {
+
+template<typename T>
+class DirectedRootedTree : public Tree<T> {
+public:
+  DirectedRootedTree() = default;
+
+  DirectedRootedTree(std::map<T, std::set<T>> G)
+    : Tree<T>::Tree(G) {}
+};
+
+} // namespace tree
+
+#endif