Why all the elements are shown in dissection tree?

I have developed my own plugin in wireshark using lua. In dissection tree when we click at first time it is showing all the elements of the tree (till in the depth root item, child, grand child). I want that at first click it should see only level 1 (root level) information only.

I have seen below questions and referred.

1. https://ask.wireshark.org/questions/42404/lua-dissector-tree-collapse
2. https://ask.wireshark.org/questions/31356/how-to-get-all-tree-items-collapsed-as-default-in-gtk-version

I tried the solution which is mentioned by @Hadriel in second question (related to ett value) but it isnot applied. can anyone look into this?