TreeNode* mergeTrees(TreeNode* root1, TreeNode* root2) {
if(root1==nullptr){
return root2;
}else if(root2==nullptr){
return root1;
}
TreeNode* root=new TreeNode(root1->val + root2->val);
root->left=mergeTrees(root1->left,root2->left);
root->right=mergeTrees(root1->right,root2->right);
return root;
}