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: repo_tree.go
    path of file: ./repos/gitea/modules/git
    
    the code of the file until where you have to start completion: // Copyright 2015 The Gogs Authors. All rights reserved.
// Copyright 2019 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package git

import (
	"bytes"
	"os"
	"strings"
	"time"
)

// CommitTreeOpts represents the possible options to CommitTree
type CommitTreeOpts struct {
	Parents    []string
	Message    string
	KeyID      string
	NoGPGSign  bool
	AlwaysSign bool
}

// CommitTree creates a commit from a given tree id for the user with provided message
func (repo *Repository) CommitTree(author, committer *Signature, tree *Tree, opts CommitTreeOpts) (ObjectID, error) {
	commitTimeStr := time.Now().Format(time.RFC3339)

	// Because this may call hooks we should pass in the en
    
func (repo *Repository) CommitTree(author, committer *Signature, tree *Tree, opts CommitTreeOpts) (ObjectID, error) {
	commitTimeStr := time.Now().Format(time.RFC3339)

	// Because this may call hooks we should pass in the environment
	env := append(os.Environ(),
		"GIT_AUTHOR_NAME="+author.Name,
		"GIT_AUTHOR_EMAIL="+author.Email,
		"GIT_AUTHOR_DATE="+commitTimeStr,
		"GIT_COMMITTER_NAME="+committer.Name,
		"GIT_COMMITTER_EMAIL="+committer.Email,
		"GIT_COMMITTER_DATE="+commitTimeStr,
	)
	cmd := NewCommand(repo.Ctx, "commit-tree").AddDynamicArguments(tree.ID.String())

	for _, parent := range opts.Parents {
		cmd.AddArguments("-p").AddDynamicArguments(parent)
	}

	messageBytes := new(bytes.Buffer)
	_, _ = messageBytes.WriteString(opts.Message)
	_, _ = messageBytes.WriteString("\n")

	if opts.KeyID != "" || opts.AlwaysSign {
		cmd.AddOptionFormat("-S%s", opts.KeyID)
	}

	if opts.NoGPGSign {
		cmd.AddArguments("--no-gpg-sign")
	}

	stdout := new(bytes.Buffer)
	stderr := new(bytes.Buffer)
	err := cmd.Run(&RunOpts{
		Env:    env,
		Dir:    repo.Path,
		Stdin:  messageBytes,
		Stdout: stdout,
		Stderr: stderr,
	})
	if err != nil {
		return nil, ConcatenateError(err, stderr.String())
	}
	return NewIDFromString(strings.TrimSpace(stdout.String()))
}