Lets Suppose I have 

```
ID A1 B1  A2  B2
1  3  4   5   6
2  7  8   9   10

```

I want to use pandas stack and wants to achieve something like this

```
ID A B
1  3 4
1  5 6
2  7 8
2  9 10

```

but what I got is 

```
ID  A   B
1   3   4
2   7   8
1   5   6
2   9   10

```

this is what i am using

```
df.stack().reset_index().

```

Is it possible to achieve something like this using Stack? `append()` method in pandas does this, but if possible I want to achieve using `pandas` `stack()` Any idea ?