Strange ambiguous between . in Add(TValue) and Add(params IEnumerable<TValue>)

[zms9110750]

I don't understand why he appeared//CS0121

TreeNode<int> a = new TreeNode<int>(4);
a.Add(1);//CS0121
		 //IOrderedTreeExtension.extension<TValue, TNode>(IOrderedTree<TValue, TNode>).Add(TValue)
		 //IOrderedTreeExtension.extension<TValue, TNode>(IOrderedTree<TValue, TNode>).Add(params IEnumerable<TValue>)

I am unable to reproduce it

B<int> b = new B<int>();
b.Add(1); // OK

static class P
{
	extension<T>(B<T> x)
	{
		public void Add(T i) { }
		public void Add(params IEnumerable<T> i) { }
	}
}
class B<T>;

so , source code in here
when

		public TNode? AddVertically(Index index, params IEnumerable<TValue> nodes)
		{
			using var e = nodes.GetEnumerator();
			if (!e.MoveNext())
			{
				return default;
			}
			var currentNode = instance.AddAt(index, e.Current);
			while (e.MoveNext())
			{
				currentNode = currentNode.Add(value: e.Current);   // here , if delete parameter name , then //CS0121
			}
			return currentNode;
		}