Hi,

Odoo supports unlimited levels of sub-entities (companies within companies) in its multi-company setup. So if your structure is:

Holding Company

└── Sub-Holding A

    └── Operating Company A1

    └── Operating Company A2

└── Sub-Holding B

    └── Operating Company B1

        └── Subsidiary B1.1

            └── Subsidiary B1.1.1

This is fully supported in Odoo. You can create as many hierarchical levels as needed.

Hope it helps