```
public TreeNode sortedArrayToBST(int[] nums) {
TreeNode head = helper(nums,0,nums.length-1);
return head;
}
public TreeNode helper(int[] nums, int start, int end){
if(start > end) return null;
int mid = start + (end - start) / 2;
TreeNode node = new TreeNode(nums[mid]);
node.left = helper(nums,start,mid-1);
node.right = helper(nums,mid+1,end);
return node;
}
```