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change/@itwin-tree-widget-react-944faa0b-268a-40c9-9ae5-49d45b91b7c7.json

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+{
+  "type": "minor",
+  "comment": "`CategoriesTree` component rendered `Categories` as a flat list, where each `Category` had zero or more child `SubCategories`. Some iTwin.js applications started to group `Categories` under `DefinitionContainers` and wanted to see them displayed in `CategoriesTree` component. Added `DefinitionContainers` to `CategoriesTree` component. This change doesn't affect applications that don't have `DefinitionContainers`.",
+  "packageName": "@itwin/tree-widget-react",
+  "email": "100586436+JonasDov@users.noreply.github.com",
+  "dependentChangeType": "patch"
+}