/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
class Solution {
public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
if(t1==null)
return t2;
if(t2==null)
return t1;
t1.val+=t2.val;
t1.left=mergeTrees(t1.left,t2.left);
t1.right=mergeTrees(t1.right,t2.right);
return t1;
}
}