> For the complete documentation index, see [llms.txt](https://engyon.gitbook.io/engyon/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://engyon.gitbook.io/engyon/en/reference/group-audits/complex-structures-tree-structures.md).
# Complex structures ('tree structures')
On Settings → audit units, users can link multiple layers of group audits via the tree structure. Engyon also supports complex group structures. Group structures may have multiple layers, with each layer representing its own group audit. In such cases, it must be possible to link a group audit to another group audit, and to link yet another group audit to that linked group audit. As a result of this complex tree structure, objects (processes, systems, risks, test plans, etc.) must be shareable with multiple group audits so they only need to be defined once.
When dealing with a complex structure, first create the audit units and coupled audits in Settings → audit units. Then click on the tree icon to create the links between the audit units.
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**Note:** it is essential that **all** audit units and **all** coupled audits are created at the top of the tree: directly under the 'highest' audit that was created first. This also applies to audits located (much) lower in the tree.
At the top of the tree, an audit unit must be created for all legal entities (it is possible to combine multiple legal entities into one audit unit; entities for which coupled audits (financial statements/entities for which an independent auditor's report is issued) are created must always form an audit unit individually). Even if these entities are located much lower in the tree. This makes it possible, for example, to define risks and procedures at the top of the tree that need to be performed much lower.
The coupled audits must also be created at the top of the tree (and linked to the correct audit unit). This ensures that the risks and procedures at the top of the tree can also be shared with the coupled audits of entities that are much lower in the tree.
When the user clicks the 'tree' icon, Engyon automatically creates the correct audit units in all coupled audits (taking into account the client's structure and the audit units defined at the top of the tree) and links the correct audits to those audit units. Once the top of the tree is defined, Engyon automatically sets up the rest of the tree.
If this approach is deviated from, the linking functionality between audits will not work sufficiently, and Engyon cannot be used optimally to achieve productivity improvements in complex engagements.
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