It could be this, i.e. the shape of a leaf/feather:

Type # 8. Pinnate Drainage Pattern:
Pinnate pattern is developed in a narrow valley flanked by steep ranges. The tributaries originating from the steep sides of parallel ridges join the longtitudinal master consequent occupying the valley at acute angles (fig. 17.14). The drainage network of the upper Son and Narmada rivers denotes the example of pinnate drainage pattern. This pattern resembles the veins of a leaf.
https://www.geographynotes.com/drainage-system/10-main-types...

IDENTIFYING AND DESCRIBING DRAINAGE PATTERNS
There different drainage patterns e.g
 Dendritic pattern (tree like river with its branches)
 Trellis/rectangular pattern (main river and tributaries flow along
faulted areas
 Parallel pattern (rivers flow opposite in each other for a long distance)
 Radial pattern (cycle wheel like rivers from a dome to different
directions)
 Centripetal pattern (rivers pouring in to one basin)
 Pinnate pattern (feather like river as tributaries flow from one direction
to the main river)
http://www.caltecacademy.com/notes/s.6/S.4, S.5, S.6 Geograp...

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Note added at 1 hr (2023-02-16 12:22:03 GMT)
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Pinnation occurs in certain waterway systems in which all major tributary streams enter the main channels by flowing in one direction at an oblique angle.
Pinnation (also called pennation) is the arrangement of feather-like or multi-divided features arising from both sides of a common axis. Pinnation occurs in biological morphology, in crystals,[1] such as some forms of ice or metal crystals,[2][3] and in patterns of erosion or stream beds.[4]
The term derives from the Latin word pinna meaning "feather", "wing", or "fin".
https://en.wikipedia.org/wiki/Pinnation

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Note added at 5 days (2023-02-21 20:41:03 GMT) Post-grading
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Glad to be of help!