Leaflet v1 plugin: layer control for ungrouped, grouped, and nested-grouped layers

Question

I need a Leaflet plugin which extends L.Control.Layers. I have the following requirements:

• works with Leaflet 1.x
• handles ungrouped layers alongside grouped ones
• handles nested layer groups
• does not rely on actual Leaflet LayerGroups, but can be built up independently (in other words, layers can be grouped in this control in a different structure to how the layers themselves are grouped in the Leaflet map)

I've tried:

• https://github.com/ismyrnow/leaflet-groupedlayercontrol (doesn't seem to handle ungrouped layers)
• https://github.com/stefanocudini/leaflet-panel-layers (can't get it to work at all)
• https://github.com/robbiet480/leaflet-categorized-layers (also can't get this to work)

Can anyone suggest if any plugin does what I need?

BOUNTY ADDED To qualify for the bounty, please link to or upload a fully working example using Leaflet 1.x, including in the custom layer control:

• ungrouped layers
• grouped layers
• nested groups