class Solution {
public:
    TreeNode* mergeTrees(TreeNode* t1, TreeNode* t2) {
        if(t1 == NULL)
            return t2;
        if(t2 == NULL)
            return t1;
        TreeNode *res = new TreeNode(t1->val+t2->val);
        res->left = mergeTrees(t1->left,t2->left);
        res->right = mergeTrees(t1->right,t2->right);
        return res;
    }
};