Binding data to a nested ListView

You can use Parent ListView OnItemDataBound event, and bind Child ListView.

<asp:ListView ID="DatabaseListView" runat="server"
    OnItemDataBound="DatabaseListView_ItemDataBound">
    <ItemTemplate>
        <h1><%# Eval("Name") %></h1>
        <asp:ListView ID="CompanyListView" runat="server">
            <ItemTemplate>
                <p><%# Eval("Name") %></p>
            </ItemTemplate>
        </asp:ListView>
        <hr />
    </ItemTemplate>
</asp:ListView>

Code Behind

public class Database
{
    public string Name { get; set; }

    public IList<Company> Companies;

    public Database()
    {
        Companies = new List<Company>();
    }
}

public class Company
{
    public string Name { get; set; }
}

protected void Page_Load(object sender, EventArgs e)
{
    if (!IsPostBack)
    {
        var databases = new List<Database>
        {
            new Database
            {
                Name = "Database 1 Name",
                Companies = new List<Company>
                {
                    new Company {Name = "123"},
                    new Company {Name = "Abc"}
                }
            },
            new Database
            {
                Name = "Database 2 Name",
                Companies = new List<Company> {new Company {Name = "Xyz"}}
            },
            new Database
            {
                Name = "Database 3 Name",
                Companies = new List<Company> {new Company {Name = "Test"}}
            },
        };

        DatabaseListView.DataSource = databases;
        DatabaseListView.DataBind();
    }
}

protected void DatabaseListView_ItemDataBound(object sender, ListViewItemEventArgs e)
{
    if (e.Item.ItemType == ListViewItemType.DataItem)
    {
        var database = e.Item.DataItem as Database;
        var companyListView = e.Item.FindControl("CompanyListView") as ListView;

        companyListView.DataSource = database.Companies;
        companyListView.DataBind();
    }
}