<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0609</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2026-10-26</periodOfReport>

    <issuer>
        <issuerCik>0002076561</issuerCik>
        <issuerName>Pine Tree Acquisition Corp.</issuerName>
        <issuerTradingSymbol>PAXG</issuerTradingSymbol>
        <issuerForeignTradingSymbol></issuerForeignTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0002104909</rptOwnerCik>
            <rptOwnerName>Pine Tree Sponsor Group, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerNonUSAddressFlag>false</rptOwnerNonUSAddressFlag>
            <rptOwnerStreet1>C/O PINE TREE ACQUISITION CORP.</rptOwnerStreet1>
            <rptOwnerStreet2>418 BROADWAY, #6538</rptOwnerStreet2>
            <rptOwnerCity>ALBANY</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>12207</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <aff10b5One>0</aff10b5One>

    <derivativeTable>
        <derivativeTransaction>
            <securityTitle>
                <value>Class B Ordinary Shares</value>
            </securityTitle>
            <conversionOrExercisePrice>
                <value>0</value>
            </conversionOrExercisePrice>
            <transactionDate>
                <value>2026-10-26</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>D</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
                <footnoteId id="F1"/>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>385714</value>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>D</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <exerciseDate>
                <footnoteId id="F2"/>
            </exerciseDate>
            <expirationDate>
                <footnoteId id="F2"/>
            </expirationDate>
            <underlyingSecurity>
                <underlyingSecurityTitle>
                    <value>Class A Ordinary Shares</value>
                </underlyingSecurityTitle>
                <underlyingSecurityShares>
                    <value>385714</value>
                </underlyingSecurityShares>
            </underlyingSecurity>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>4542857</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </derivativeTransaction>
    </derivativeTable>

    <footnotes>
        <footnote id="F1">Represents shares forfeited by the reporting person as a result of the underwriters of the Issuer's initial public offering (the &quot;IPO&quot;) terminating the remaining portion of the over-allotment option of the IPO.</footnote>
        <footnote id="F2">The Class B ordinary shares of the Issuer are convertible into the Issuer's Class A ordinary shares concurrently with or immediately following the consummation of an initial business combination, or earlier at the option of the holders thereof on a one-for-one basis, subject to the adjustments. The Class B ordinary shares have no expiration date.</footnote>
    </footnotes>

    <ownerSignature>
        <signatureName>/s/ Pine Tree Sponsor Group, LLC by Pine Tree Top, LLC, Manager</signatureName>
        <signatureDate>2026-10-26</signatureDate>
    </ownerSignature>
</ownershipDocument>
