Trees and BST in C#

public class TreeNode {
    public int val;
    public TreeNode left;
    public TreeNode right;
    public TreeNode(int val = 0, TreeNode left = null, TreeNode right = null) {
        this.val = val;
        this.left = left;
        this.right = right;
    }
}

public void Inorder(TreeNode root) {
    if (root == null) return;
    Inorder(root.left);
    Console.Write(root.val + " ");
    Inorder(root.right);
}