If you are using the block form of the {{x-tree}} component, the expand/collapse toggle and the checkbox are no longer included in the custom HTML. Furthermore, the value yielded is no longer the model for the node, but an object containing the model and the components that are included.
To upgrade, convert:
{{#x-tree
model=tree
checkable=true
as |node|
}}
{{node.name}}
{{/x-tree}}
to
{{#x-tree
model=tree
checkable=true
as |node|
}}
{{node.toggle}}
{{node.checkbox}}
{{node.model.name}}
{{/x-tree}}