The most common and most likely answer to this crossword clue is the 2 plus 5 letter word AT FIRST
I've seen this crossword clue in The Guardian
A
T
F
I
R
S
T
More clues leading to the result AT FIRST
- Originally a way to contain disagreement arising
- Trees in a thicket cleared initially
- A way to snort crack up before anything else
- Trees in middle of Seattle to start with
- Initially put evergreens in allotment — left, right, and centre
- A thirst with following for Hearts to begin with
- Trees planted in middle of Seattle, initially
- Initially provided set up in new start
- American, leader of team leading early on
- Start if planned in the early stages
Buddy explains!

The straight part
We know that "to start with" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case to start with = at first.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.