You can create an organisation overall budget by summing the Business Unit Budgets using the Consolidation setting:
Navigate to the Budgets & Actuals screen
In the Budget you are working on, select the Organisation name, with the Block of Flat icon to the left
Then at the top of the screen on the right Click on CONSOLIDATE
Choose the Business Unit Category that you wish to Consolidate
SAVE CHANGES
This will then populate the Organisation screen with the sum of all the Business Unit Budgets within that Type.
Please note, Calxa can only sum one Business Unit Category to give the overall Organisation value.