Controlling rule-based labelling using PyQGIS?

Below some help to setup rule based labeling from scratch with the new QGIS 3 API

#Configure label settings
settings = QgsPalLayerSettings()
settings.fieldName = 'myFieldName'
textFormat = QgsTextFormat()
textFormat.setSize(10)
settings.setFormat(textFormat)
#create and append a new rule
root = QgsRuleBasedLabeling.Rule(QgsPalLayerSettings())
rule = QgsRuleBasedLabeling.Rule(settings)
rule.setDescription(fieldName)
rule.setFilterExpression('myExpression')
root.appendChild(rule)
#Apply label configuration
rules = QgsRuleBasedLabeling(root)
myLayer.setLabeling(rules)
myLayer.triggerRepaint()

Unfortunately I can't find how to iterate over existing rules, the labeling() method available for vector layers return an object of QgsAbstractVectorLayerLabeling class but it seems there is no way to get the root rule (QgsRuleBasedLabeling) from this class, the only possibility I found is to get directly pal settings using providers ids but I can't access to rules tree. Anyone have a clue ?

EDIT

It's now fixed, labeling() function return a QgsRuleBasedLabeling() : https://github.com/qgis/QGIS/commit/4b365a8f47d96b35f7609859e580388927ae0606

From QGIS 3, there is a new QgsRuleBasedLabeling Class which would allow you to control rule-based labelling using the new API.

Rules can be added using QgsRuleBasedLabeling::Rule.

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(Unfortunately, I cannot test the 2.99 version at the moment. But I would happily accept an answer if it provides a working example.)