BottomBar should be fixed if popup menu clicked


I have a page called menu1 which is my home screen. I have bottom bar in which i have 5 icons. If i select first icon, 4 menus will open . If i select menu 1, it should display menu1screen and in that case bottombar should remain constant.Similarly if i change other menus in popup, it should display it respective screens. How can i acheive this scenario?

I need to acheive the scenario as per in image attached.

Any help as i am new to flutter!!