Adding group items to Layout legend using PyQGIS

Question

I want to add to the Print Layout Legend groups, subgroups, and layers using PyQGIS like in the picture:

But I can only add layers:

root = QgsLayerTree()
layers_ =  self.qgis_project.mapLayers().values()

for layer_ in layers_:
    if layer_.type() == QgsMapLayer.VectorLayer:
        if len(list(layer_.getFeatures())) != 0:
            self.root.addLayer(layer_)

legend.model().setRootGroup(self.root)

I tried to create a group and add the group to the model:

root = QgsLayerTree()
root_group = QgsProject.instance().layerTreeRoot()
group = root_group.findGroup("Group")
subgroup1 = group.findGroup("Subgroup1")
root.addGroup("Subgroup1")

for layer_ in subgroup1.children():
    root.addLayer(layer_)

legend.model().setRootGroup(self.root)

But I get an error:

TypeError: QgsLayerTreeGroup.addLayer(): argument 1 has unexpected
type 'QgsLayerTreeLayer'

How can I create Legend Items like in the picture with groups, subgroups, and layers?

Answer 1

You are just missing a call to get the QgsMapLayer from the QgsLayerTreeLayer which is what QgsLayerTreeGroup.addLayer() expects:

root = QgsLayerTree()
root_group = QgsProject.instance().layerTreeRoot()
group = root_group.findGroup("Group")
subgroup1 = group.findGroup("Subgroup1")
root.addGroup("Subgroup1")

for layer_ in subgroup1.children():
    root.addLayer(layer_.layer())  # CHANGE IS HERE

legend.model().setRootGroup(self.root)