Multiple menus in sidebar - how to create “push” effect?

[stackerito]

I have a sidebar and whenever I click a category I want the main category menu to be "pushed" away by the sub-category menu, and vice versa (when clicking "Go back" button)

So far I managed to make the main category menu to be pushed, but the sub-category menu just shows at the bottom of the menu, then "waits" for the transition of the main category menu to to finish and then it jumps to top.

Demo: https://codepen.io/Stackerito/pen/dyWmBrV
Also, I wonder if this is the correct logic for multiple menus in a sidebar, or I should work on a totally different implementation?

Thanks!