import algorithm, future, macros, math, sequtils, sets, strutils, tables

macro unpack(rhs: seq, cnt: static[int]): auto =
  let t = genSym(); result = quote do:(let `t` = `rhs`;())
  if NimMinor <= 17:
    for i in 0..<cnt: result[0][1].add(quote do:`t`[`i`])
  else:
    for i in 0..<cnt: result[1].add(quote do:`t`[`i`])

template input(T: typedesc, cnt: Natural = 1): untyped =
  let line = stdin.readLine.split(" ")
  when T is int:         line.map(parseInt).unpack(cnt)
  elif T is float:       line.map(parseFloat).unpack(cnt)
  elif T is string:      line.unpack(cnt)
  elif T is char:        line.mapIt(it[0]).unpack(cnt)
  elif T is seq[int]:    line.map(parseint)
  elif T is seq[float]:  line.map(parseFloat)
  elif T is seq[string]: line
  elif T is seq[char]:   line.mapIt(it[0])

proc `&=`(n: var int, m: int) = n = n and m
proc `|=`(n: var int, m: int) = n = n or m
proc `%=`(n: var int, m: int) = n = n mod m
proc `//=`(n: var int, m: int) = n = n div m
proc `<<=`(n: var int, m: int) = n = n shl m
proc `>>=`(n: var int, m: int) = n = n shr m
proc `<?=`(n: var SomeNumber, m: SomeNumber) = n = min(n, m)
proc `>?=`(n: var SomeNumber, m: SomeNumber) = n = max(n, m)
proc newSeq2[T](n1, n2: Natural): seq[seq[T]] = newSeqWith(n1, newSeq[T](n2))
proc newSeq3[T](n1, n2, n3: Natural): seq[seq[seq[T]]] = newSeqWith(n1, newSeqWith(n2, newSeq[T](n3)))

# -------------------------------------------------- #

const P = 10 ^ 9 + 7
var (N, K) = input(int, 2)
var edge = newseq2[int](N + 1, 0)
for i in 1 .. N - 1:
  var (a, b) = input(int, 2)
  inc a; inc b;
  edge[a].add(b)
  edge[b].add(a)
proc dfs(v: int, p: int): seq[int] =
  result = @[1]
  for u in edge[v]:
    if u == p: continue
    var subtree = dfs(u, v)
    var A = result.len()
    var B = subtree.len()
    var newResult = newseq[int](A + B - 1)
    for i in 0 .. A - 1:
      for j in 0 .. B - 1:
        newResult[i + j] += (result[i] * subtree[j]) mod P
        newResult[i + j] %= P
    result = newResult
  result.add(1)
echo dfs(1, 0)[K]