By default for more than 5 items, ListPicker switches to full screen mode.But if you don't want full screen mode,then we need to set ItemCountThresholdProperty after 'InitializeComponent();' in c# like this
ListPickerDataSync.SetValue(Microsoft.Phone.Controls.ListPicker.ItemCountThresholdProperty, 10);
Note:ItemCountThresholdProperty will not work if you set it using xaml