diff --git a/README.md b/README.md
index 1e6ba6f..cb15a05 100644
--- a/README.md
+++ b/README.md
@@ -56,209 +56,26 @@ julia> for batch in t
 (a = [4, 1, 2], b = Bool[1, 0, 1])
 ```
 
-### `AbstractTrace`
+**Traces**
 
-`Trace` is the most commonly used `AbstractTrace`. It provides a sequential view on other containers.
+- `Traces`
+- `MultiplexTraces`
+- `CircularSARTTraces`
+- `Episode`
+- `Episodes`
 
-```julia
-julia> t = Trace([1,2,3])
-3-element Trace{Vector{Int64}, SubArray{Int64, 0, Vector{Int64}, Tuple{Int64}, true}}:
- 1
- 2
- 3
-julia> push!(t, 4)
-4-element Vector{Int64}:
- 1
- 2
- 3
- 4
-
-julia> append!(t, 5:6)
-6-element Vector{Int64}:
- 1
- 2
- 3
- 4
- 5
- 6
-
-julia> pop!(t)
-6
-
-julia> popfirst!(t)
-1
-
-julia> t
-4-element Trace{Vector{Int64}, SubArray{Int64, 0, Vector{Int64}, Tuple{Int64}, true}}:
- 2
- 3
- 4
- 5
-
-julia> empty!(t)
-Int64[]
-
-julia> t
-0-element Trace{Vector{Int64}, SubArray{Int64, 0, Vector{Int64}, Tuple{Int64}, true}}
-```
-
-In most cases, it's just the same with a `Vector`.
-
-When an `AbstractArray` with higher dimension provided, it is **slice**d along the last dimension to provide a sequential view.
-
-```julia
-julia> t = Trace(rand(2,3))
-3-element Trace{Matrix{Float64}, SubArray{Float64, 1, Matrix{Float64}, Tuple{Base.Slice{Base.OneTo{Int64}}, Int64}, true}}:
- [0.276012181224494, 0.6621365818458671]
- [0.9937726056924112, 0.3308302850028162]
- [0.9856543000075456, 0.6123660950650406]
-
-julia> t[1]
-2-element view(::Matrix{Float64}, :, 1) with eltype Float64:
- 0.276012181224494
- 0.6621365818458671
-
-julia> t[1] = [0., 1.]
-2-element Vector{Float64}:
- 0.0
- 1.0
-
-julia> t
-3-element Trace{Matrix{Float64}, SubArray{Float64, 1, Matrix{Float64}, Tuple{Base.Slice{Base.OneTo{Int64}}, Int64}, true}}:
- [0.0, 1.0]
- [0.9937726056924112, 0.3308302850028162]
- [0.9856543000075456, 0.6123660950650406]
-
-julia> t[[2,3,1]]
-2×3 view(::Matrix{Float64}, :, [2, 3, 1]) with eltype Float64:
- 0.993773  0.985654  0.0
- 0.33083   0.612366  1.0
-```
-
-**Note** that when indexing a `Trace`, a **view** is returned. As you can see above, the data is modified in-place.
-
-### `AbstractTraces`
-
-`Traces` is one of the common `AbstractTraces`. It is similar to a `NamedTuple` of several traces.
-
-```julia
-julia> t = Traces(;
-           a=[1, 2],
-           b=Bool[0, 1]
-       )  # note that `a` and `b` are converted into `Trace` implicitly
-Traces with 2 traces:
-  :a => 2-element Trace{Vector{Int64}, SubArray{Int64, 0, Vector{Int64}, Tuple{Int64}, true}}
-  :b => 2-element Trace{Vector{Bool}, SubArray{Bool, 0, Vector{Bool}, Tuple{Int64}, true}}
-
-
-julia> push!(t, (a=3, b=false))
+**Samplers**
 
-julia> t
-Traces with 2 traces:
-  :a => 3-element Trace{Vector{Int64}, SubArray{Int64, 0, Vector{Int64}, Tuple{Int64}, true}}
-  :b => 3-element Trace{Vector{Bool}, SubArray{Bool, 0, Vector{Bool}, Tuple{Int64}, true}}
+- `BatchSampler`
 
+**Controllers**
 
-julia> t[:a]
-3-element Trace{Vector{Int64}, SubArray{Int64, 0, Vector{Int64}, Tuple{Int64}, true}}:
- 1
- 2
- 3
+- `InsertSampleRatioController` 
+- `AsyncInsertSampleRatioController`
 
-julia> t[:b]
-3-element Trace{Vector{Bool}, SubArray{Bool, 0, Vector{Bool}, Tuple{Int64}, true}}:
- false
-  true
- false
 
-julia> t[1]
-(a = 1, b = false)
+Please refer tests for common usage. (TODO: generate docs and add links to above data structures)
 
-julia> t[1:3]
-(a = [1, 2, 3], b = Bool[0, 1, 0])
-```
-
-Another commonly used traces is `MultiplexTraces`. In reinforcement learning, *states* and *next-states* share most data except for the first and last element.
-
-```julia
-julia> t = MultiplexTraces{(:state, :next_state)}([1,2,3]);
-
-julia> t[:state]
-2-element Trace{SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, SubArray{Int64, 0, SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, Tuple{Int64}, true}}:
- 1
- 2
-
-julia> t[:next_state]
-2-element Trace{SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, SubArray{Int64, 0, SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, Tuple{Int64}, true}}:
- 2
- 3
-
-julia> push!(t, (;state=4))
-4-element Vector{Int64}:
- 1
- 2
- 3
- 4
-
-julia> t[:state]
-3-element Trace{SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, SubArray{Int64, 0, SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, Tuple{Int64}, true}}:
- 1
- 2
- 3
-
-julia> t[:next_state]
-3-element Trace{SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, SubArray{Int64, 0, SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, Tuple{Int64}, true}}:
- 2
- 3
- 4
-
-julia> length(t)
-3
-```
-
-Note that different kinds of `AbstractTraces` can be combined to form a `MergedTraces`.
-
-```
-ulia> t1 = Traces(a=Int[])
-       t2 = MultiplexTraces{(:b, :c)}(Int[])
-       t3 = t1 + t2
-MergedTraces with 3 traces:
-  :a => 0-element Trace{Vector{Int64}, SubArray{Int64, 0, Vector{Int64}, Tuple{Int64}, true}}
-  :b => 0-element Trace{SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, SubArray{Int64, 0, SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, Tuple{Int64}, true}}
-  :c => 0-element Trace{SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, SubArray{Int64, 0, SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, Tuple{Int64}, true}}
-
-
-julia> push!(t3, (a=1,b=2,c=3))
-
-julia> t3[:a]
-1-element Trace{Vector{Int64}, SubArray{Int64, 0, Vector{Int64}, Tuple{Int64}, true}}:
- 1
-
-julia> t3[:b]
-1-element Trace{SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, SubArray{Int64, 0, SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, Tuple{Int64}, true}}:
- 2
-
-julia> t3[:c]
-1-element Trace{SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, SubArray{Int64, 0, SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, Tuple{Int64}, true}}:
- 3
-
-julia> push!(t3, (a=-1, b=-2))
-
-julia> t3[:a]
-2-element Trace{Vector{Int64}, SubArray{Int64, 0, Vector{Int64}, Tuple{Int64}, true}}:
-  1
- -1
-
-julia> t3[:b]
-2-element Trace{SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, SubArray{Int64, 0, SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, Tuple{Int64}, true}}:
- 2
- 3
-
-julia> t3[:c]
-2-element Trace{SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, SubArray{Int64, 0, SubArray{Int64, 1, Vector{Int64}, Tuple{UnitRange{Int64}}, true}, Tuple{Int64}, true}}:
-  3
- -2
-```
 ## Acknowledgement
 
 This async version is mainly inspired by [deepmind/reverb](https://github.com/deepmind/reverb). 
diff --git a/test/common.jl b/test/common.jl
index 091d587..444c3fc 100644
--- a/test/common.jl
+++ b/test/common.jl
@@ -1,3 +1,29 @@
+@testset "sum_tree" begin
+    t = SumTree(8)
+
+    for i in 1:4
+        push!(t, i)
+    end
+
+    @test length(t) == 4
+    @test size(t) == (4,)
+
+    for i in 5:16
+        push!(t, i)
+    end
+
+    @test length(t) == 8
+    @test size(t) == (8,)
+    @test t == 9:16
+
+    t[:] .= 1
+    @test t == ones(8)
+    @test all([get(t, v)[1] == i for (i, v) in enumerate(0.5:1.0:8)])
+
+    empty!(t)
+    @test length(t) == 0
+end
+
 @testset "CircularArraySARTTraces" begin
     t = CircularArraySARTTraces(;
         capacity=3,