Added level order traversal, and more nodes in main method

data_structures/Trees/TreeTraversal.java

@@ -1,3 +1,5 @@
+import java.util.LinkedList;
+
 /**
  *
  * @author Varun Upadhyay (https://github.com/varunu28)
@@ -9,19 +11,27 @@ public class TreeTraversal {
     public static void main(String[] args) {
         Node tree = new Node(5);
         tree.insert(3);
+        tree.insert(2);
         tree.insert(7);
+        tree.insert(4);
+        tree.insert(6);
+        tree.insert(8);
 
-        // Prints 3 5 7
-        tree.printInOrder();
+        System.out.println("Pre order traversal:");
+        tree.printPreOrder();
         System.out.println();
 
-        // Prints 5 3 7
-        tree.printPreOrder();
+        System.out.println("In order traversal:");
+        tree.printInOrder();
         System.out.println();
 
-        // Prints 3 7 5
+        System.out.println("Post order traversal:");
         tree.printPostOrder();
         System.out.println();
+
+        System.out.println("Level order traversal:");
+        tree.printLevelOrder();
+        System.out.println();
     }
 }
 
@@ -88,5 +98,19 @@ public void printPostOrder() {
         }
         System.out.print(data + " ");
     }
-}
 
+    public void printLevelOrder() {
+  		LinkedList<Node> queue = new LinkedList<>();
+  		queue.add(this);
+  		while (queue.size() > 0) {
+  			Node head = queue.remove();
+  			System.out.print(head.data + " ");
+  			if (head.left != null) {
+  				queue.add(head.left);
+  			}
+  			if (head.right != null) {
+  				queue.add(head.right);
+  			}
+  		}
+  	}
+}