tree_format prints invalid graph

[mcrumiller]

Checks

• I have checked that this issue has not already been reported.
• I have confirmed this bug exists on the latest version of Polars.

Reproducible example

from polars import col, int_range
expr = (col("a") + col("b"))**2 + int_range(3)
expr.meta.tree_format()

Log output

0                  1           2              3                  4              5
   ┌────────────────────────────────────────────────────────────────────────────────────────────────────
   │
   │      ╭───────────╮
 0 │      │ binary: + │
   │      ╰───────────╯
   │            │ ╰─────────────────╮      ────╮    ──────────╮
   │            │                                             │
   │            │                                             │
   │ ╭─────────────────────╮                          ╭───────────────╮
 1 │ │ function: int_range │                          │ function: pow │
   │ ╰─────────────────────╯                          ╰───────────────╯
   │            │ ╰─────────────────╮──────────╮    ──────────╮──────────────────╮
   │            │                   │                         │                  │
   │            │                   │                         │                  │
   │       ╭────────╮          ╭────────╮                ╭────────╮        ╭───────────╮
 2 │       │ lit(3) │          │ lit(0) │                │ lit(2) │        │ binary: + │
   │       ╰────────╯          ╰────────╯                ╰────────╯        ╰───────────╯
   │                                                                             │ ╰─────────────╮
   │                                                                             │               │
   │                                                                             │               │
   │                                                                        ╭────────╮      ╭────────╮
 3 │                                                                        │ col(b) │      │ col(a) │
   │                                                                        ╰────────╯      ╰────────╯

Issue description

I haven't dived into the details, but sometimes the graph that is returned is invalid.

Related to #11176 most likely.

Expected behavior

Should produce valid graph.

Installed versions

--------Version info---------
Polars:               0.20.4
Index type:           UInt32
Platform:             Linux-5.15.133.1-microsoft-standard-WSL2-x86_64-with-glibc2.35
Python:               3.11.3 (main, Apr 15 2023, 14:44:51) [GCC 11.3.0]

----Optional dependencies----
adbc_driver_manager:  0.8.0
cloudpickle:          3.0.0
connectorx:           0.3.2
deltalake:            0.15.0
fsspec:               2023.12.2
gevent:               23.9.1
hvplot:               0.9.1
matplotlib:           3.8.2
numpy:                1.26.3
openpyxl:             3.1.2
pandas:               2.1.4
pyarrow:              14.0.2
pydantic:             2.5.3
pyiceberg:            0.5.1
pyxlsb:               1.0.10
sqlalchemy:           2.0.25
xlsx2csv:             0.8.1
xlsxwriter:           3.1.9