Loading data for a bus into Simulink involves two parts: the data itself and a definition of the bus data type.
For the data itself, you use your structure. The Bus object(s) you're creating define the bus data type. I believe you're seeing more than one bus object because your structure includes nested structures (which correspond to a nested bus). With a nested bus, you need to define the data type for that element of the bus using another Bus object.
To use your structure in the Constant block, you should be able to specify the value using the name of the variable in the workspace (could be base workspace or model workspace) with the structure data and then define the Output data type as Bus: myBusObject where myBusObject is the name of the Bus object for the top-level bus. You'll find the Output data type parameter for the Constant block on the Signal Attributes tab of the block dialog.
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