The TreeList widget does not have detailTemplate functionality and I have to say that there is no workaround that we could suggest for implementing this.
As for alternative component, the Grid widget is the one that renders detailTemplate, but it will be difficult to match the columns structure of the parent Grid with all of the nested Grids in the detailTemplate (assuming there will be more than one level).
If any other questions on this matter arise, please do not hesitate to contact us again.
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