Why roslyn#9606 would be ambiguous

Query.cs

void Main()
{
	var a = new C();
	
	// var x = a? +a? +a : a;

	var x = (a != null) +a? +a : a;
	var y = a? (+a != null) +a : a;
}

class C
{
	public static C operator+(C c)
	{
		return c;
	}
	
	public static C operator+(C c1, C c2)
	{
		return c1;
	}

	public static C operator+(bool b, C c2)
	{
		return c2;
	}
	
	public static implicit operator bool(C c)
	{
		return true;
	}
}