convert array to bst

class Solution {
    TreeNode* sortedArrayToBST(vector<int>& nums, int start, int end){
        if(end<=start) return NULL;
        int midIdx=(end+start)/2;
        TreeNode* root=new TreeNode(nums[midIdx]);
        root->left=sortedArrayToBST(nums, start, midIdx);
        root->right=sortedArrayToBST(nums, midIdx+1,end);
        return root;
    }
public:
    TreeNode* sortedArrayToBST(vector<int>& nums) {
        return sortedArrayToBST(nums, 0,nums.size());
    }
};