package main

import (
	"bufio"
	"fmt"
	"io"
	"math"
	"os"
	"strconv"
	"strings"

)


func main() {
	solve(os.Stdin, os.Stdout)
}

type ReaderEx struct {
	baseScanner *bufio.Scanner
	words       []string
	nextWordIdx func() int
	initWordIdx func()
}

func NewScannerEx(stdin io.Reader) *ReaderEx {
	var this ReaderEx
	var idx int
	this.baseScanner = bufio.NewScanner(stdin)
	this.baseScanner.Buffer(make([]byte, 0), 1E+11)
	this.nextWordIdx = func() int {
		cur := idx
		idx++
		return cur
	}
	this.initWordIdx = func() {
		idx = 0
	}
	return &this
}

func (me *ReaderEx) Scan(doSplit bool) (isScanned bool) {
	isScanned = me.baseScanner.Scan()
	if doSplit {
		me.words = strings.Fields(me.baseScanner.Text())
	} else {
		me.words = []string{me.baseScanner.Text()}
	}
	me.initWordIdx()
	return
}

func (me *ReaderEx) nextBytes() []byte {
	return []byte(me.words[me.nextWordIdx()])
}
func (me *ReaderEx) nextString() string {
	return me.words[me.nextWordIdx()]
}

type StringArray []string

func (me *ReaderEx) nextStringArray() StringArray {
	return me.words[me.nextWordIdx():]
}

func (me StringArray) toStrings() []string {
	return me
}

func (me StringArray) toInts() []int {
	strValues := me.toStrings()
	values := make([]int, len(strValues))
	for i, v := range strValues {
		n, err := strconv.Atoi(v)
		if err != nil {
			panic(err)
		}
		values[i] = n
	}
	return values
}
func (me *ReaderEx) nextInt() int {
	n, err := strconv.Atoi(me.words[me.nextWordIdx()])

	defer func() {
		if err != nil {
			panic(fmt.Sprintf("getInt(%d)", n))
		}
	}()
	return n
}

func pow(x, y, mod int) (ans int) {

	ans = 1
	for bit := 1 << uint(math.Floor(math.Log2(float64(y)))); ; bit >>= 1 {
		if y&bit != 0 {
			ans *= x
			if mod > 0 {
				ans %= mod
			}
		}
		if bit <= 1 {
			return
		}
		ans *= ans
		if mod > 0 {
			ans %= mod
		}
	}
}

type factType struct {
	prime int
	count int
}

func fact(n int) (facts []*factType) {

	for i := 2; i*i <= n; i++ {
		if n%i == 0 {
			fa := factType{prime: i}
			for n%fa.prime == 0 {
				n /= fa.prime
				fa.count++
			}
			facts = append(facts, &fa)
		}
	}
	if n > 1 {
		facts = append(facts, &factType{prime: n, count: 1})
	}
	return facts
}
func dec2bin(n int) (ret []bool) {
	for bit := 1 << uint(math.Floor(math.Log2(float64(n)))); ; bit >>= 1 {
		ret = append(ret, n&bit != 0)

		if bit <= 1 {
			return
		}
	}

}

func abs(v int) int {
	if v < 0 {
		v = -v
	}
	return v
}

func b2i(b bool) (i int) {
	if b {
		i = 1
	} else {
		i = 0
	}
	return
}

//Edge is
type Edge struct {
	node *Node
	line *Line
}

//Node is
type Node struct {
	id    int
	edges []*Edge
}

//Line is
type Line struct {
	edges []Edge
}

//NewLine is
func NewLine(a, b *Node) (line *Line) {
	line = &Line{}
	line.edges = []Edge{{node: a, line: line}, {node: b, line: line}}
	a.edges = append(a.edges, &line.edges[1])
	b.edges = append(b.edges, &line.edges[0])
	return
}

//Another is
func (edge *Edge) Another() (another *Edge) {
	line := edge.line
	if &line.edges[0] == edge {
		another = &line.edges[1]
	} else {
		another = &line.edges[0]
	}
	return
}

func solve(stdin io.Reader, stdout io.Writer) {

	r := NewScannerEx(stdin)
	r.Scan(true)
	n, k := r.nextInt(), r.nextInt()
	nodes := make([]Node, n+1)
	//lines := make([]*Line, 0)

	for i := 1; i <= n; i++ {
		nodes[i] = Node{id: i}
	}

	for i, end := 1, n-1; i <= end; i++ {
		r.Scan(true)
		NewLine(&nodes[r.nextInt()], &nodes[r.nextInt()])
	}

	mod := pow(10, 9, 0) + 7

	type nodePack struct {
		pre   *Node
		node  *Node
		level int
	}
	ans := k
	nodeList := []nodePack{{nil, &nodes[1], 1}}

loop:
	for len(nodeList) > 0 {
		cur := nodeList[len(nodeList)-1]
		nodeList = nodeList[0 : len(nodeList)-1]

		p := k - []int{2, 1}[b2i(cur.level <= 1)]
		for _, next := range cur.node.edges {
			if next.node == cur.pre {
				continue
			}
			if p < 0 {
				ans = 0
				break loop
			}
			ans = ans * p % mod
			p--
			nodeList = append(nodeList, nodePack{cur.node, next.node, cur.level + 1})
		}
	}

	fmt.Fprintln(stdout, ans)

}


Measured memory_bytes: 29312