any function for merge two YAML::Node

[cxwx]

Is there any feature for merging two node
just like https://neovim.io/doc/user/lua/#vim.tbl_deep_extend() ?

[SGSSGene]

No, there is no such function/feature also we are not planning to implement this. You would need to implement your own.

We are currently discussion a feature of merging keys #1279, but this would only support shallow merging and not deep/recursive merging as you are requesting.
The biggest issue is the definition of a unique key in the yaml specs which might even make an implementation behave unexpectedly.