انا بقلم الغصن.

Because in this sentence it is being understood as the verb بقلّم = I trim / I am trimming, not the preposition+noun phrase بِقلم = with a pen.

Arabic writing often leaves out:

• short vowels
• the shadda (the doubling mark)

So بقلم can look ambiguous on the page. For a learner, a clearer spelling would be أنا بقلّم الغصن.

In Egyptian Arabic, بـ is a very common marker for the present tense.

So:

• قلّم = he trimmed / trim! depending context
• بقلّم = I trim / I am trimming

In Egyptian, this بـ often gives a present or habitual meaning, and in many everyday contexts it can also be used for something happening right now.

Because أنا is optional here.

The verb already shows the subject, so بقلّم الغصن can already mean I trim the branch. Adding أنا can:

• make the subject clearer
• add emphasis
• create contrast, like I’m the one trimming the branch

So both are possible, but أنا is not strictly necessary.

The basic verb is قلّم.

It means things like:

• to trim
• to prune
• to clip

So with الغصن (the branch), the idea is to prune/trim the branch.

This is a doubled verb, which is why teachers often write it with a shadda: قلّم.

غصن means branch or twig.

The الـ at the beginning means the, so:

• غصن = a branch
• الغصن = the branch

In this sentence, الغصن is the direct object of the verb: it is the thing being trimmed.

It is Egyptian-style because of the present-tense verb pattern with بـ.

A Standard Arabic version would look more like:

• أنا أُقَلِّمُ الغُصْنَ

In Egyptian Arabic, that becomes:

• أنا بقلّم الغصن

So the بـ is one of the big clues that this is colloquial Egyptian rather than Modern Standard Arabic.

A helpful approximate pronunciation is:

ana baʔallim il-ghoṣn

A few notes:

• أنا = ana
• بقلّم in Cairo is often pronounced with ق as a glottal stop, so something like baʔallim
• الـ is often heard as il- or el-
• غ is like a French/German-style throaty gh

So you may also see a learner-friendly spelling like:

• ana ba'allim el-ghosn

Because normal Arabic writing usually leaves out most pronunciation marks.

That means learners often have to infer the correct reading from:

• context
• vocabulary
• grammar

So a native reader may easily understand بقلم from context, but a learner may need a more explicit version such as:

• أنا بقلّم الغصن

This is very normal in Arabic writing.

Yes. You can simply say:

بقلّم الغصن

That is a very natural way to say it if the subject is already understood. Adding أنا is fine too, especially if you want emphasis or clarity.

Yes, غصن is understandable and natural for branch/twig, especially for a tree or plant branch.

Depending on context, Egyptians might also use other words, but غصن is absolutely a real and usable word. So the unusual-looking part of the sentence is not الغصن itself; the main issue for learners is that بقلم is ambiguous in writing unless you know it is being read as بقلّم.