Added code for Binary Tree Inorder Traversal

TreeNode.java

@@ -0,0 +1,39 @@
+ public class TreeNode {
+     int val;
+     TreeNode left;
+     TreeNode right;
+      TreeNode() {}
+     TreeNode(int val) { this.val = val; }
+     TreeNode(int val, TreeNode left, TreeNode right) {
+         this.val = val;
+         this.left = left;
+         this.right = right;
+     }
+ }
+
+class Solution {
+
+    public List<Integer> preHelper(TreeNode root, List<Integer> list){
+
+        if(root == null){
+            return list;
+        }
+
+        preHelper(root.left, list);
+        list.add(root.val);
+        preHelper(root.right, list);
+
+        return list;
+    }
+
+
+
+    public List<Integer> inorderTraversal(TreeNode root) {
+
+        List<Integer> list = new ArrayList<>();
+
+        return preHelper(root, list);
+
+
+    }
+}