Tool bar items on master page adding multiple times

Tool bar items on master page adding multiple times.

Here is code

var Logo = new ToolbarItem
{
Icon = "logo.png",
Text = "",
};
var tUserName = new ToolbarItem
{
Icon = "",
Text = "Hi, " + Helper.GetUserId(),
};
this.ToolbarItems.Clear();
this.ToolbarItems.Add(tUserName);
this.ToolbarItems.Add(Logo);

When i logged to App for the first time tool bar items are adding but after logout and login same toll bar adding two times