Add Binary Search Tree (BST) (#159)

Author: piyushkumar0707

DIRECTORY.md

@@ -34,6 +34,8 @@
   * [K Folds](https://github.com/TheAlgorithms/R/blob/HEAD/data_preprocessing/k_folds.r)
   * [Lasso](https://github.com/TheAlgorithms/R/blob/HEAD/data_preprocessing/lasso.r)
 
+## Data Structures
+  * [Binary Search Tree](https://github.com/TheAlgorithms/R/blob/HEAD/data_structures/binary_search_tree.r)
 ## Graph Algorithms
   * [Dijkstra Shortest Path](https://github.com/TheAlgorithms/R/blob/HEAD/graph_algorithms/dijkstra_shortest_path.r)
   * [Breadth First Search](https://github.com/TheAlgorithms/R/blob/HEAD/graph_algorithms/breadth_first_search.r)