Merge Two Binary Trees LeetCode solution in Python

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/**
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 * Definition for a binary tree node.
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 * struct TreeNode {
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 *     int val;
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 *     TreeNode *left;
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 *     TreeNode *right;
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 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
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 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
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 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
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 * };
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 */
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class Solution {
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public:
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    TreeNode* mergeTrees(TreeNode* root1, TreeNode* root2) {
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        if(root1==NULL) return root2;
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        if(root2==NULL) return root1;
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        root1->val+=root2->val;
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        root1->left=mergeTrees(root1->left,root2->left);
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        root1->right=mergeTrees(root1->right,root2->right);
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        return root1;
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    }
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};