Instead of synchronizing the whole account tree on each data changed take advantage of the new, more granular, signals and perform the appropriate modifications in the model's data after it has been loaded once.
Also create a separate instance for the institutions model. This change has the following rationale. Mixing the two hierarchies in the same model (by account type and institution) would make it difficult to implement changes since depending on the changes it would imply structural modifications in only one instance of the same account. So for example changing the institution means a structural change in the institution hierarchy but no change in the accounts by type hierarchy. Separating the two hierarchies means that one account can be found only once in the model and it also simplifies the implementation of the modifications slots.

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