Closest to Binary Tree[Easy] C#

Approach: Use binary search to find the elements and keep updating the closest starting from the root being the closest. return closest

using System;

public class Program {
    public static int FindClosestValueInBst(BST tree, int target) 
    {
        return FindClosestValueInBST(tree, target, tree.value);
    }
    public static int FindClosestValueInBST(BST tree, int target, int closest)
    {
        if(Math.Abs(target - closest) > Math.Abs(target-tree.value)){
            closest = tree.value;
        }
        if(target < tree.value && tree.left != null)
        {
            return FindClosestValueInBST(tree.left, target, closest);
        }
        else if(target > tree.value && tree.right != null)
        {
            return FindClosestValueInBST(tree.right, target, closest);
        }
        else
        {
            return closest;
        }
    }

    public class BST {
        public int value;
        public BST left;
        public BST right;

        public BST(int value) {
            this.value = value;
        }
    }
}