see-617. Merge Two Binary Trees

TreeNode* mergeTrees(TreeNode* t1, TreeNode* t2) {
        if(t1==NULL&&t2==NULL)
        	return t1;
        if(t1&&t2)
        {
            t1->val +=t2->val;
        	t1->left=mergeTrees(t1->left,t2->left);
            t1->right=mergeTrees(t1->right,t2->right);        	
        }
        if(t1==NULL)
        {
        	return t2;
        }
        return t1;

    }