层级树：数组描述的递归建树

-- 错误：手写固定层数的展开，加层就失灵
local a = build(data[1])
local b = build(data[2])

local function buildTree(tree, out)
    local childCount = tree[1]
    if childCount == nil then return end
    local rest = {}
    for i = 2, #tree do
        rest[#rest + 1] = tree[i]
    end
    for i = 1, childCount do
        out.data[i] = {val = 0, data = {}}
        buildTree(rest[i], out.data[i])
    end
end