Trie in kotlin, Insert, find and fetch

Trie.kt

fun main() {
    var trie = Trie()
    Trie.insert(trie, "hello", "hi", "hey", "","   *") //Inserting "hello", "hi", "hey" into the trie, "*" will be replace by empty string
    println(Trie.find(trie, "hey")) //checking out if "hey exists inside the trie"
    println(Trie.fetch(trie)) // traversing the trie and get all the words inside of it and printing them
}


class Trie(var node: MutableMap<Char, Trie> = mutableMapOf()){

    companion object {
        fun insert(trie: Trie, vararg words: String) {
            words.map{
                it.replace("*","")}
                .filter { it.isNotEmpty()}
                .forEach {
                _insert(trie, it)
            }
        }

        private fun _insert(trie: Trie, word: String) {
            if (word.isEmpty()) {
                trie.node['*'] = Trie()
                return
            }
            val c = word[0]
            if (!trie.node.contains(c)) {
                trie.node[c] = Trie()
            }
            _insert(trie.node[c]!!, word.substring(1))
        }

        fun find(trie: Trie, word: String): Boolean {
            if (word.isEmpty()) {
                return true
            }

            val c = word[0]
            if (!trie.node.containsKey(c)) {
                return false
            }
            return find(trie.node[c]!!, word.substring(1))
        }

        fun fetch(trie: Trie): MutableList<String> {
            val list = mutableListOf<String>()
            trie.node.forEach { entry ->
                if (entry.key == '*') {
                    list.add("")
                } else {
                    fetch(entry.value).forEach { s ->
                        val string = entry.key + s
                        list.add(string)
                    }
                }
            }
            return list
        }
    }


}