def read_tree(treeish, opts = {})
      arr_opts = []
      arr_opts << "--prefix=#{opts[:prefix]}" if opts[:prefix]
      arr_opts += [treeish]
      command('read-tree', arr_opts)
    end
def read_tree(treeish, opts = {})
      arr_opts = []
      arr_opts << "--prefix=#{opts[:prefix]}" if opts[:prefix]
      arr_opts += [treeish]
      command('read-tree', arr_opts)
    end
reads a tree into the current index file