public static BinaryTreeNode BuildBinarySearchTree(int[] sortedArray)
{
    if (sortedArray.Length == 0)
        return null;
 
    int _mid = sortedArray.Length / 2;
    BinaryTreeNode _root = new BinaryTreeNode(sortedArray[_mid]);
    int[] _left = GetSubArray(sortedArray, 0, _mid - 1);
    int[] _right = GetSubArray(sortedArray, _mid + 1, sortedArray.Length - 1);
    _root.Left = BuildBinarySearchTree(_left);
    _root.Right = BuildBinarySearchTree(_right);
 
    return _root;
}
 
 
public int[] GetSubArray(int[] array, int start, int end)
{
    List<int> _result = new List<int>();
    for (int i = start; i <= end; i++)
    {
        _result.Add(array[i]);
    }
    return _result.ToArray();
}