You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: parse_tree.go
    path of file: ./repos/trickster/vendor/github.com/influxdata/influxql
    
    the code of the file until where you have to start completion: package influxql

import (
	"fmt"
)

var Language = &ParseTree{}

type ParseTree struct {
	Handlers map[Token]func(*Parser) (Statement, error)
	Tokens   map[Token]*ParseTree
	Keys
    
func (t *ParseTree) Group(tokens ...Token) *ParseTree {
	for _, tok := range tokens {
		// Look for the parse tree for this token.
		if subtree := t.Tokens[tok]; subtree != nil {
			t = subtree
			continue
		}

		// No subtree exists yet. Verify that we don't have a conflicting
		// statement.
		if _, conflict := t.Handlers[tok]; conflict {
			panic(fmt.Sprintf("conflict for token %s", tok))
		}

		// Create the new parse tree and register it inside of this one for
		// later reference.
		newT := &ParseTree{}
		if t.Tokens == nil {
			t.Tokens = make(map[Token]*ParseTree)
		}
		t.Tokens[tok] = newT
		t.Keys = append(t.Keys, tok.String())
		t = newT
	}
	return t
}