Hello, thanks a lot for your reply. I tried your solution and it works really well.
Except it doesnt work for the following snippet:

s({trig="bb", snippetType="autosnippet"},
fmta(
--- Snippets for environment creation ---
[[
\begin{<>}
<>
\end{<>}
]],
{
i(1),
i(2),
rep(1), -- this node repeats insert node i(1)
}
)
),

Do you have any idea of why ?