private ImmutableList <T> InsertImpl(int index, IEnumerable <T> items)
{
if (this.root == null)
{
return(new ImmutableList <T>(LeafSegment.MakeLeaf(items)));
}
else
{
var segs = this.root.Insert(index, items);
if (segs.Length == 1)
{
return(new ImmutableList <T>(segs[0]));
}
else
{
return(new ImmutableList <T>(new TreeSegment(segs)));
}
}
}
