Function insert 

pub fn insert<K: Clone + Ord, V, O: OwnerMut<Map<K, V>>>(
    owner: O,
    key: K,
    value: V,
) -> Option<MapHandle<K, V, O>>

Inserts a key-value pair into a map, returning a handle to the data if successful. A result of None indicates that either the map could not be accessed or the key already exists.