How to add multiple levels to "category" so that blocks can be displayed in the preview floating window?

Hi! I want to achieve such a feature: when the mouse moves over a block, the floating window displays its next level blocks. As shown below: I made a floating window div, but I don’t know how to display the blocks in the floating window. I read about BlockManager.render() in the documentation, but it can only control where the blocks are displayed, I don't think it is an appropriate way. I would like to ask if there are other solutions? Hope someone can answer this question, thank you very much!